IARC

In brief

What IARC is

The International Agency for Research on Cancer, IARC, is the World Health Organization's (WHO's) specialized cancer agency, established in 1965 on the premise that finding and preventing the causes of cancer needs coordinated international science beyond the reach of any single country ¹. It is based in Lyon, France ¹. A Governing Council that represents the participating states sets its policy and appoints both the Director and a Scientific Council of independent scientists, who serve four-year terms without pay ³. IARC is funded mainly by contributions from its participating states, about two dozen countries whose number has grown with recent accessions, together with competitive research grants; in 2015 that core came chiefly from member governments, and in 2026 its leadership warned of constrained core funding and growing reliance on short-term earmarked money ^1,3. Recent members include Egypt and Saudi Arabia, and Portugal, which joined in 2025 ¹.

The agency does several jobs that are easy to confuse: its Monographs decide whether an agent can cause cancer in people, a task called hazard identification, which IARC describes as the essential first step in cancer prevention ⁴. A separate series, the Handbooks of Cancer Prevention, asks the opposite question, whether an action lowers cancer risk, such as avoiding excess body fat or taxing alcohol ^11,15. Its surveillance teams estimate how many cancers occur worldwide and how many each cause accounts for, using GLOBOCAN, its database of national cancer estimates, and the registries collected in Cancer Incidence in Five Continents ⁹. It also publishes the World Cancer Report for a general readership ^16,17.

The Monographs are what reaches the news, and through Volume 119 they had evaluated more than 1,000 agents and found 120 of them to be carcinogenic to humans, meaning able to cause cancer in people ⁵. By 2026 that count had reached 135, with 24 agents placed in the top group for the first time in the 15 years after the last full review of that group ⁸. The agents range from industrial chemicals and medicines to occupations, personal habits such as drinking alcohol, radiation and infections ^5,15.

None of these ratings is a statement about how much cancer an exposure causes ⁴. A Group 1 label on processed meat and the same label on sulfur mustard gas tell the reader one identical thing about each, that the evidence of a causal link is strong, and nothing about which does more harm ^4,14. The agency's critics and its defenders agree on that much; they disagree about whether a rating that leaves out dose is still useful to the public ^3,14.

The full history

IARC was created on 20 May 1965 by a resolution of the World Health Assembly, after French public figures urged President Charles de Gaulle to have nations commit a small share of military spending to cancer research; its founding participating states were France, the Federal Republic of Germany, Italy, the United Kingdom and the United States, and Lyon, France, offered to host it ^1,21. Within a few years it had turned to the work it is best known for ^1,3,4. Shortly after its founding, the World Health Organization asked it to list the agents known to cause cancer in humans, and Lorenzo Tomatis, then chief of IARC's Division of Carcinogenicity, launched a systematic process to decide what belonged on the list ³. IARC dates the program's inception to 1971 and its first Monograph to 1972, which is why both years appear in accounts of its founding ^3,4,22. The agency has had six directors: John Higginson (1966 to 1981), Lorenzo Tomatis (1982 to 1993), Paul Kleihues (1994 to 2003), Peter Boyle (2004 to 2008), Christopher Wild (2009 to 2018) and Elisabete Weiderpass (since 2019) ^21,22,23.

The rules hardened in stages, beginning with the Preamble, the standing rulebook printed at the front of every volume, which took shape in the late 1970s ¹². From 1982 a positive result in short-term tests for DNA damage could raise an overall evaluation, and in 1991 a working group set out when mechanistic evidence could move an agent up or down a category ⁴. The 2006 Preamble tightened the handling of conflicts of interest and defined the roles of everyone at a meeting ⁴. The 2019 revision, prepared by an advisory group of 21 members from nine countries after a six-month public comment period, rebuilt the way evidence is combined ^4,12.

The parasites entered early: Volume 61, from a Working Group that met in Lyon from 7 to 14 June 1994, evaluated the schistosomes, the liver flukes and the stomach bacterium Helicobacter pylori together ²⁴. Volume 100, compiled in 2008 and 2009 and published in 2012, reviewed the 107 agents in Group 1 as of 2009, a count that includes agents such as C. sinensis that it newly placed there, with the infectious ones in its Part B ^6,19,25. The conclusions for those biological agents were announced in April 2009, three years before the 441-page book appeared, which is why the same parasite decisions carry two dates, 2009 and 2012 ^25,26.

The list of human carcinogens has grown rather than shrunk: Volume 100 began with the 107 agents in Group 1 as of 2009 and ended with 111, 114 were listed by 2015, 128 by March 2024 and 135 in 2026, 24 of them added since Volume 100 ^3,6,7,8. As of 2015, no Group 1 agent had been moved down by a later Working Group, although the Volume 100 review gave every one of them a second hearing ³. Ratings below Group 1 have moved in both directions as evidence arrived, up for C. sinensis, PFOA, talc and hepatitis D virus and down for coffee, and the timeline marks each reversal ^3,20,27,28.

How a rating is made, step by step

Anyone can start the process: nominations come from national regulators, scientists, public-health workers, industry and private citizens, and IARC periodically opens a public call for them ³. An Advisory Group of outside scientists then sifts the nominations and recommends priorities for the next five years: one group set them in 2019 for 2020 to 2024, and in March 2024, 28 independent scientists from 22 countries considered more than 200 candidate agents for 2025 to 2029 ^7,52. Priority goes to agents with evidence of current human exposure and enough published evidence to support a new or updated evaluation ⁷. IARC staff make the final choice of what to evaluate and when ³. The list is not closed: the 2024 Advisory Group advised that an agent may be given priority within the five-year window if compelling new evidence of an emerging carcinogenic hazard appears ⁷.

IARC staff then assemble a Working Group, the panel that will make the decision, by searching the literature for experts and asking the scientific community and earlier advisory groups for names ³. The list of proposed members and their declared interests is posted publicly before the meeting so that anyone can comment ^3,18. Conflicts are judged mainly on financial ties, though public statements and positions on the agent also count, and members are asked not to consult on the agent until the volume is published ⁴. People with a conflict of interest cannot serve as voting Working Group members; an expert whose knowledge is essential may still take part as an invited specialist, who joins the discussion but does not draft the evaluation or vote, and interested organizations may send observers, who may also have conflicts ^3,4,53. About a year before each meeting, IARC posts the meeting and its agents on the Monographs website with a public call for experts, a call for data and a deadline for observers to apply ⁵³.

Five kinds of people sit in the room ⁴. Working Group members are unpaid, are not employed by IARC and alone make the evaluation; IARC's own staff, called the Secretariat, organize the work and check that the rules are followed but do not decide the outcome ³. Invited specialists, experts whose knowledge is needed but who have conflicts of interest that bar them from Working Group membership, take part without drafting the evaluation or voting; representatives attend from national and international health agencies, and observers attend from interested organizations and may have conflicts of interest of their own ^3,4,53. To limit the pull of any one expert's own research, each study summary is drafted or checked by a member who had no part in that study ⁴.

Preparation takes about 12 months and ends in a meeting of about eight days in Lyon ¹⁸. Subgroups review the human, animal and mechanistic evidence, and the whole group then debates in plenary before reaching an overall evaluation ^3,4. The Working Group votes; many votes are unanimous, and minority views are sometimes written into the record, as when a small minority of the 2025 panel judged the evidence on how cytomegalovirus might cause cancer strong enough for Group 2A ^3,10. A short summary appears in The Lancet Oncology soon after the meeting, and the full Monograph follows later, three years later in the case of the 2009 parasite decisions ^10,25,26,27.

One step is missing by design: the conclusions are not sent to an outside panel for independent peer review, which critics affiliated with the chemical industry count as a weakness that survived the 2019 revision ⁵⁴. IARC's defenders answer that the process is transparent from nomination to vote and that disagreement among scientists is not evidence that it failed ³.

Three streams of evidence and the rules that combine them

Every evaluation weighs three streams: studies of cancer in people, studies of cancer in experimental animals, and mechanistic evidence on how the agent might cause cancer, with human exposure described alongside ⁴. Human and animal evidence are each rated sufficient, limited or inadequate, and mechanistic evidence is rated strong, limited or inadequate ⁴. Sufficient human evidence means a positive association in which chance, bias and confounding, a third factor that creates a false link, have been ruled out with reasonable confidence; limited means a causal reading is credible but those explanations could not be ruled out ⁴.

Mechanistic evidence is organized around ten key characteristics named at two IARC workshops in 2012, drawing on the Group 1 agents reviewed in Volume 100: being electrophilic, meaning chemically reactive with DNA, directly or after the body converts it; being genotoxic, damaging DNA; altering DNA repair; inducing epigenetic changes, which alter how genes are switched on without changing their sequence; inducing oxidative stress; inducing chronic inflammation; suppressing immunity; acting through cell receptors; immortalizing cells; and altering cell growth, death or nutrient supply ³³. Among 86 Group 1 agents the commonest characteristic was genotoxicity, and agents showed an average of four ⁵. For the liver flukes, the cancer is generally attributed to chronic inflammation ³⁰.

Since 2019 the three streams are combined in a single step, rather than mechanisms being considered after a preliminary verdict ^3,4. Group 1 requires sufficient evidence in humans or, exceptionally, sufficient evidence in animals together with strong mechanistic evidence in exposed people ⁴. Group 2A generally requires two of three findings, limited human evidence, sufficient animal evidence and strong mechanistic evidence, with at least one of them coming from people or human cells ⁴. Group 2B requires one of those findings, and an agent that meets none of the routes goes to Group 3 ⁴.

Recent decisions show the rules at work: PFOA, perfluorooctanoic acid, reached Group 1 in 2023 on sufficient animal evidence and strong mechanistic evidence in exposed people, with human cancer evidence only limited, while its chemical cousin PFOS, perfluorooctanesulfonic acid, long used in firefighting foams and stain repellents, with strong mechanistic evidence alone, went to 2B ²⁰. In 2025 the herbicides atrazine and alachlor went to 2A on limited human, sufficient animal and strong mechanistic evidence, while the fungicide vinclozolin, with no human signal, stopped at 2B ⁵⁵. Of the 24 agents newly placed in Group 1 since Volume 100, all but two, PFOA and dioxin-like PCBs, had sufficient evidence in humans ⁸. The PFOA decision drew criticism: consultants at Gradient argued in 2024 that the human associations were weak and inconsistent, that the animal results were driven by benign tumors, and that the key characteristics were used as a checklist ⁵⁶.

It is tempting to read the 2019 changes as letting mechanisms decide on their own, and they do not: strong mechanistic evidence alone cannot make an agent Group 1 ⁴. On its own it supports Group 2B, or Group 2A only when the agent belongs to a mechanistic class whose members are already in Group 1 or 2A ⁴. What did change in 2019 is that an evaluation can now proceed with no animal data at all ¹².

The 2019 Preamble also cut the categories from five to four ⁴. Group 4, probably not carcinogenic to humans, held a single agent, caprolactam, a chemical used to make nylon, as of 2015 ³. Because IARC only evaluates agents with some suggestion of carcinogenicity, Group 4 was folded into Group 3, and Working Groups may now add the words probably not carcinogenic when the evidence warrants ⁴. A Group 3 rating is not a finding of safety; it often means the agent's carcinogenic potential is unknown and there are prominent gaps in the research ⁴. Some reviews still describe four groups, including Group 4, years after the change ⁵⁷.

Hazard, not risk

IARC's own rulebook draws the line: hazard is the strength of the evidence that an agent is a carcinogen; risk is the probability that a given exposure to that carcinogen will result in cancer ⁴. The series, long titled IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, was renamed in 2019 the IARC Monographs on the Identification of Carcinogenic Hazards to Humans, to reflect exactly that difference ^4,24. Hazard identification does not predict how large a risk is under particular conditions; only information on how risk rises with dose can do that ³.

So a Group 1 rating says how sure the panel is that something can cause cancer, and nothing about how much cancer it causes ⁴. The numbers show the gap: a 2025 analysis estimated that eating processed meat raises colorectal-cancer risk by at least 7% on average and rated that evidence weak, two stars out of five ⁵⁹, while in a pooled analysis of 13,169 lung-cancer cases men who smoked more than 30 cigarettes a day had on the order of 20 to 100 times the odds of lung cancer of never-smokers, depending on tumor type ⁶⁰; both agents are in Group 1. Critics put the consequence sharply: hazard-only schemes place agents of wildly different strength side by side, which is how eating processed meat can fall into the same category as sulfur mustard gas ¹⁴. They argue this breeds health scares, needless costs and the loss of useful products, and they want an internationally agreed method that weighs dose and exposure ¹⁴. That paper's authors included a scientist at Syngenta, a pesticide manufacturer, and several private consultants ¹⁴.

IARC's defenders answer that hazard identification is meant to come first, with regulators and other bodies assessing risk afterward ^3,4. In 2015 more than 100 scientists, many of them former Working Group members, examined the criticisms of the process and judged them unconvincing ³. They pointed out that of 970 agents considered in 111 volumes, 52% landed in Group 3 and only 12% in Group 1, which is not the pattern of a process tilted toward finding carcinogens ³.

The aspartame decision of July 2023 shows two bodies doing two jobs: IARC rated the sweetener 2B on the strength of the evidence, while the Joint FAO/WHO Expert Committee on Food Additives (JECFA), which sets acceptable intake levels, completed its own evaluation the same month and reaffirmed aspartame's safety, calling the human evidence not convincing ^40,41. The two findings answer different questions, whether aspartame could cause cancer and whether ordinary intake does, so both can stand ^4,41.

What happens after a rating is up to others: national and international authorities use IARC's evaluations to support actions that cut exposure, and across 30 country reports in IARC's Impact in Practice series the asbestos classification recurred as an evaluation that helped give regulation, worker protection and compensation a common scientific basis ^1,4. Regulators may also disagree: most pesticide regulators have not followed IARC on glyphosate ^36,61.

How IARC counts cancers, and what it says prevents them

Separately from the Monographs, IARC estimates how many cancers occur and how many each cause accounts for ⁹. Its figures put new cancer cases worldwide at 20 million in 2024, with 35 million predicted by 2050 from population aging alone ⁹. The central tool is the population-attributable fraction, the share of a population's cancers that would not have occurred without a given cause ⁹. Saracci and Vineis warned in 2011 that any such fraction is specific to the population it describes and is best read as a pointer to impact rather than a precise measurement ²².

For infections, IARC's October 2026 analysis estimated 2.3 million new cancers in 2024, 12% of all cases ⁹. H. pylori accounted for 760,000 cases, human papillomavirus 750,000, hepatitis B virus 360,000, Epstein-Barr virus 260,000 and hepatitis C virus 160,000 ⁹. Eastern Asia carried 990,000 of the cases, 42% of the total, and low- and middle-income countries carried 77% ⁹. IARC's previous estimate, for 2018, had put the share at about 13%, or 2.2 million cases, and the new analysis added 16 infection-cancer pairs, though the authors caution that changes in data sources make the two figures not directly comparable ⁹.

The figures are no better than the registries beneath them ⁹. High-quality population registries in the latest edition of Cancer Incidence in Five Continents covered about 19% of the world's population and 2% of Africa's, and the authors published no uncertainty intervals because they found no reliable way to combine their varied data sources ⁹. They also note that methods for identifying bacterial and parasitic carcinogens are less standardized than those for viruses, and that gaps in coverage could push their estimates too low or too high in under-represented regions ⁹.

The World Cancer Report gathers such estimates for policymakers and the public: its first edition, in 2003, projected a rise from 10 million new cases in 2000 to 15 million in 2020, and later editions appeared in 2008, 2014 and 2020 ^16,17. The Handbooks of Cancer Prevention, running since the late 1990s, ask whether an action lowers risk ^11,15. In 2016 a Working Group found sufficient evidence that the absence of excess body fat lowers the risk of 13 cancers, eight more than a 2002 group had identified, while noting that most of the evidence came from observational studies rather than weight-loss trials ¹¹. Volume 20 of the Handbooks dealt with alcohol in two parts: Volume 20A, in 2023, examined how reducing or stopping alcohol affects cancer risk ⁶², and Volume 20B, in 2025, concluded that higher taxes, minimum prices, limits on sales and strong marketing bans reduce drinking ¹⁵. In 2026 IARC Working Groups also reported on programs that test for and treat H. pylori to prevent stomach cancer and on lung-cancer screening ^63,64.

Handbook conclusions draw criticism too: a 2025 systematic review argued that IARC's 2015 evaluation of mammography relied on observational studies in which women who attended screening also had a 46% lower risk of dying from causes other than breast cancer, a sign that attenders differ from non-attenders rather than proof that screening saved them, and asked for the 2015 recommendations to be revised ⁶⁵. IARC's Handbooks lead and other screening researchers replied in the same journal ^66,67.

The controversies, with each side's best case

IARC's evaluations draw fierce criticism, and some of it lands ^3,54. Critics, several writing with industry affiliations, attack the hazard-only design, the absence of outside peer review and the choice of experts ^14,54. Defenders, many of them former Working Group members, answer that the process is transparent and that disagreement is not failure ³. Both camps include people with interests worth naming: a pesticide-company scientist and chemical-industry staff among the critics, and, among the authors of IARC's own account of its rules, a scientist who disclosed work as a plaintiff's expert witness in talc litigation ^4,14,54. On glyphosate, two scientists quoted here in IARC's defense also had roles in the Roundup litigation: Christopher Portier, lead author of the 2016 rebuttal to the EU regulators, attended the 2015 glyphosate meeting as an invited specialist and later consulted for plaintiffs' lawyers ^18,68, and Dennis Weisenburger, author of the 2025 review, served as a plaintiffs' expert witness ³⁶.

One structural choice cuts both ways: IARC deliberately recruits scientists who have published on the agent under review, and the 2019 rules add safeguards against what they call careerism, such as having a study summarized by someone with no part in it ⁴. Critics see the same practice as a conflict of interest ³. In 2023, for example, two authors of the NutriNet-Santé cohort, one of the studies the panel weighed, sat on the Working Group, and the cohort's lead author attended as part of the IARC Secretariat ^40,69. The cases below give the decision, the strongest argument on each side, and where the evidence stands now.

Every parasite IARC has rated, 1994 to 2026

Seven parasites appear in the IARC Monographs. Six are flukes, parasitic flatworms: three blood flukes, Schistosoma haematobium, S. japonicum and S. mansoni, and three liver flukes, Opisthorchis viverrini, O. felineus and Clonorchis sinensis ⁹⁰. The seventh is a single-celled parasite, the malaria parasite Plasmodium falciparum, placed in Group 2A in 2012 ⁹¹. All six flukes were evaluated in Volume 61 in 1994 ²⁴. Volume 100B reviewed the biological agents in Group 1 and raised C. sinensis into it ^6,19, so the three flukes rated below Group 1 still carry their 1994 ratings, as reviews published from 2021 to 2026 confirm ^57,58,92.

S. haematobium, the blood fluke that lodges in the wall of the bladder, has the oldest case ²⁹. Its link to bladder cancer was suspected in 1905 and supported by 40 Cairo autopsies in 1911, and the excess of squamous cell carcinoma, a bladder cancer of the flat lining cells, in endemic areas pointed the same way; firm evidence came decades later from case-control studies adjusted for age, sex, type of dwelling and smoking ²⁹. It was in Group 1 in 1994 and was confirmed there in Volume 100B ^9,24,25. Mechanistic work in people adds weight: urine from 40 Angolans with urogenital schistosomiasis, half of whom also had bladder cancer, contained estrogen-derived metabolites, including DNA adducts (chemicals bound to DNA) not reported in healthy people's urine, and all 40 samples carried products of oxidative DNA damage ⁹³. IARC attributes about 5,900 bladder cancers in 2024, a third of squamous cell bladder cancers, to the fluke ⁹.

O. viverrini, caught from raw or undercooked freshwater fish in Southeast Asia, was classified Group 1 in 1994 ¹³. In Thailand, cholangiocarcinoma, cancer of the bile ducts, varied at least 12-fold between regions and tracked the prevalence of infection; in hamsters the fluke produced the cancer reliably only together with low doses of a nitrosamine, a chemical carcinogen also found in fermented fish dishes ³⁰. C. sinensis, its East Asian relative, was not considered a Group 1 carcinogen in 2007 and was classified Group 1 in 2009 ^19,30. A meta-analysis cited by Korean and IARC researchers gave a summary odds ratio, a measure of how much more common the exposure is among cases, of 4.7 (95% CI 2.2 to 9.8), and about 10% of Korean cholangiocarcinomas were attributed to the fluke ¹⁹.

Later work has held up: a 2024 meta-analysis, covering 22 studies and 34,367 participants across all liver and bile-duct outcomes, found odds ratios for cholangiocarcinoma of 4.49 (95% CI 3.43 to 5.87) for C. sinensis and 3.69 (95% CI 2.07 to 6.55) for O. viverrini ⁹⁴. In a survey of southern Laos carried out from December 2017 to February 2019 and published in 2024, 88.3% of 3,400 villagers were infected, 7.2% had ultrasound findings suggesting cholangiocarcinoma, and infection was associated with those findings, adjusted odds ratio 3.4 (95% CI 1.7 to 6.5); the endpoint was a suspicion on ultrasound, not a confirmed cancer ⁹⁵. IARC attributes about 3,800 intrahepatic cholangiocarcinomas in 2024, about 2% of all such cancers worldwide, to the two flukes ⁹.

The other three sit lower, for stated reasons: S. japonicum is in Group 2B, possibly carcinogenic, for liver and colorectal cancer ^57,96. S. mansoni is in Group 3 ⁹²; a 2021 Egyptian clinic study found that its 1,446 patients with liver cancer were more likely than 313 patients with cirrhosis but no cancer to have had past infection (adjusted odds ratio 1.59, 95% CI 1.19 to 2.13), in a population with much hepatitis C, itself a major cause of liver cancer ^9,97. For both, a 2017 review found that epidemiological studies had not produced firm evidence ²⁹. O. felineus is in Group 3: animal studies point toward a causal role, but a comparison of official statistics across 83 Russian regions found no statistically significant link with liver and bile-duct cancer: the correlation, a measure running from 0 for no relationship to 1 for a perfect one, was 0.20, and the p-value, the chance of seeing a link this strong if none existed, was 0.07, just above the usual 0.05 cutoff, so this is weak evidence either way ⁹⁸; a 2026 review argues the fluke should be re-evaluated ⁵⁸.

The other infectious Group 1 agents

IARC classes 13 infectious agents in Group 1: nine viruses, one bacterium and three parasites ⁹. Its 2026 burden analysis counted 12 of them; hepatitis D virus, added in 2025, causes liver cancer only in people who also carry hepatitis B, so its cases already sit inside the hepatitis B count ^9,10. Human immunodeficiency virus type 1, HIV-1 (HIV-2 is in Group 2B), is a special case: it raises the risk of cancers caused by other infections by weakening immunity, so the analysis counts only its conjunctival cancers, of the surface of the eye, separately ⁹.

The newest entries show the 2019 rules at work ¹⁰. Hepatitis D virus, placed in Group 3 in 1994 ⁴⁸, reached Group 1 in June 2025 on sufficient human evidence; among people with hepatitis B, a meta-analysis by the Working Group of 15 studies gave a relative risk of liver cancer of 2.13 (95% CI 1.57 to 2.87) ¹⁰. Merkel cell polyomavirus, placed in Group 2A in Volume 104 in 2012 ⁴⁹, reached Group 1 on sufficient human evidence backed by sufficient animal and strong mechanistic evidence, while cytomegalovirus went to 2B on limited evidence for childhood leukemia ¹⁰. The malaria parasite Plasmodium falciparum sits in Group 2A for Burkitt lymphoma ⁹.

What was believed and is not

Most public misreadings of IARC come from treating a statement about evidence as a statement about danger ^4,14. Others come from older versions of the rules, which changed in 2006 and again in 2019, or from assuming that related parasites must share a rating ^4,58. A third kind comes from confusing the Monographs with IARC's separate estimates of how many cancers a cause produces, which rest on different methods and carry their own uncertainty ⁹.

The cards below set each belief against what the record shows, with the year the record changed where it did. Some beliefs outlived the rules that once supported them: a 2022 review still listed Group 4 three years after it was abolished, and a 2024 meta-analysis folded O. felineus into a pooled cancer estimate with its two Group 1 relatives, and its abstract gives none for it alone ^57,94. In 2024 a comparative study of the three liver flukes still described O. felineus's Group 3 rating as noncarcinogenic to humans and called the other two Group 1A, a category IARC has never used ¹⁰⁰.

What is still unknown

Whether the three lower-rated flukes deserve their 1994 ratings is open: S. japonicum and S. mansoni have case reports, animal data and associations open to confounding but no firm epidemiology, and O. felineus has animal evidence without a demonstrated human association ^29,58,97. The Russian null finding for O. felineus comes from a comparison of regional statistics, the weakest kind of observational study, and its authors called for further work on the fluke's contribution to bile-duct cancer ⁹⁸. The pooled 2024 analysis of the liver flukes included O. felineus in its overall cholangiocarcinoma estimate, odds ratio 4.24 (95% CI 3.33 to 5.39), but gave no estimate for that species alone ⁹⁴.

How the parasites cause cancer is not settled: for S. haematobium the mechanisms remain poorly understood, partly for lack of a convenient animal model, though a more efficient mouse model and the parasite's sequenced genome are now available ²⁹. For the liver flukes, mechanical damage, parasite secretions and immune-driven inflammation all appear to contribute, and in hamsters a low dose of a nitrosamine was needed to produce cancer reliably, which leaves open how much of the human cancer is the fluke alone ³⁰. In hamsters infected side by side in 2024, precancerous changes in the bile-duct lining appeared mainly with O. viverrini, while O. felineus and C. sinensis caused similar scarring around the ducts, a hint that the species differ rather than proof about people ¹⁰¹.

The list of causes itself is incomplete: a 2026 survey of the 135 Group 1 agents found few established preventable causes for breast, prostate and colorectal cancer, three of the four commonest cancers, and read the rise of more than 20% in known human carcinogens over 15 years as a sign that preventable causes remain unrecognized ⁸. The Advisory Group's 2024 report listed ten high-priority infectious agents and judged that all 128 Group 1 agents then known deserved a systematic search for additional cancer sites ⁷.

The process questions are also live: critics still ask for standardized, documented methods for weighing studies and for outside review of Working Group conclusions, and the 2026 dispute over talc turned on how the Working Group's own bias analysis should be read ^54,83. Whether IARC can keep its scientific functions steady on constrained core funding is, in its own leadership's words, a question of gradual erosion rather than sudden failure ¹.

What IARC means for the season's question

The season asks whether the cancers attributed to parasites are the real number or only the number anyone has looked for. IARC answers one question firmly and the other only approximately: on the evidence, three flukes are established human carcinogens, rated by the same Monographs process as every other agent, though under the Preambles in force in 1994 and 2009, which the 2019 rules leave in effect ^4,24,25; how many cancers they cause is an estimate published without any uncertainty range ⁹. Their attributable cancers are small beside those of H. pylori, HPV and the hepatitis viruses: about 5,900 bladder cancers and 3,800 intrahepatic bile-duct cancers in 2024, out of 2.3 million infection-attributable cases ⁹.

Those counts are built on the thinnest data in exactly the places that matter: the highest-quality cancer registries IARC draws on covered 2% of Africa's population, where S. haematobium is mainly found, and the authors warn their estimates could be too high or too low in under-represented regions ⁹. Methods for identifying parasitic carcinogens are less standardized than those for viruses ⁹. The honest reading is that the parasite totals are estimates with unknown error in both directions, not a measured ceiling and not a proven undercount ⁹.

Neither direction of error should be overstated: the ratings rest on strong human evidence for three species and on weak or absent evidence for the other three, and no fluke has been evaluated since Volume 100B, and the only later parasite evaluation, of the malaria parasite Plasmodium falciparum in 2012, placed it in Group 2A ⁹¹; the 2025 infectious-agent meeting considered three viruses ^7,9,10. A Group 1 parasite is one the evidence shows can cause cancer; how many cancers it causes is a separate, uncertain estimate ^4,9.

Prevention is where the two halves meet: IARC's analysis names preventive treatment with praziquantel, the standard drug against flukes, often given to whole communities at once, together with clean water, sanitation and snail control as the tools against schistosome-attributable cancer ⁹. For the liver flukes, praziquantel cures the infection, but mass deworming has struggled against reinfection where raw fish remains a staple, so prevention also depends on changing how fish is prepared ^13,30.

The tests, one by one

• Epidemiological study (cohort or case-control)The human stream: a cohort study follows people forward to see who develops cancer, and a case-control study compares people with cancer against people without it, looking back at exposures ³.The only stream that can, on its own, place an agent in Group 1 ⁴.Counted as sufficient only when chance, bias and confounding have been ruled out with reasonable confidence ⁴.Weak carcinogens and low exposures are hard to detect, and false negatives may be commoner than false positives ³.
• Long-term animal bioassayThe animal stream: rodents given the agent for most of their lives, then examined for tumors ⁴.Sufficient animal evidence combined with strong mechanistic evidence in exposed people can reach Group 1, as it did for PFOA ²⁰.Of 60 Group 1 agents with tumors found in both people and animals, 52 (87%) caused tumors in at least one of the same organ or tissue systems ⁶.Doses are often higher than people encounter, and the organ affected can differ between species ^3,6.
• Key-characteristics mechanistic evidenceTen properties shared by known carcinogens, from damaging DNA to causing chronic inflammation, used to sort laboratory and human mechanistic studies ³³.Strong evidence on its own supports Group 2B, as it did for PFOS in 2023 ^4,20.Established Group 1 agents show an average of four of the ten characteristics ⁵.Non-carcinogens can also induce oxidative stress, so that characteristic is read with caution unless it occurs with others ⁴.
• Population-attributable fractionThe share of a population's cancers that would not have occurred without a given cause, used in IARC's burden estimates ⁹.Produces the estimate that infections caused 2.3 million cancers, 12% of the total, in 2024 ⁹.Published without uncertainty intervals, because the authors found no reliable way to combine their varied data sources ⁹.Only as good as the cancer data underneath it; the highest-quality registries covered about 19% of the world's population and 2% of Africa's ⁹.

Where it connects

Sources

101 sources, numbered as they are cited. Every one was checked against PubMed or its publisher before it was cited here; the note under each says what it shows and what it does not.

1. 1
   Schmütz A, Chajès V, Chauvet C, Keefe D, Weiderpass E. The International Agency for Research on Cancer: from global evidence to national action.Lancet Public Health · 2026 · 11(7):e468-e471doi:10.1016/S2468-2667(26)00091-5 · PMID 42150579

   IARC's 60th-anniversary viewpoint: dates the agency to 1965 as WHO's specialized cancer agency, names recent accessions (Egypt, Saudi Arabia, and Portugal in 2025) and describes current funding pressures; written by IARC's Director and staff with one Cancer Australia co-author, about IARC.

2. 2
   Saracci R, Wild CP. Fifty years of the International Agency for Research on Cancer (1965 to 2015).Int J Cancer · 2016 · 138(6):1309-11doi:10.1002/ijc.29929 · PMID 26613677

   Anniversary editorial by two IARC scientists; the record carries no abstract and is cited only for the founding date in its title.

3. 3
   Pearce N, Blair A, Vineis P, et al. IARC monographs: 40 years of evaluating carcinogenic hazards to humans.Environ Health Perspect · 2015 · 123(6):507-14doi:10.1289/ehp.1409149 · PMID 25712798

   More than 100 scientists, many of them former Working Group members but none IARC staff, describe how nominations, Working Groups, votes and funding worked in 2015 and reject the criticisms of the process; a defense, not a neutral audit.

4. 4
   Samet JM, Chiu WA, Cogliano V, et al. The IARC Monographs: Updated Procedures for Modern and Transparent Evidence Synthesis in Cancer Hazard Identification.J Natl Cancer Inst · 2020 · 112(1):30-37doi:10.1093/jnci/djz169 · PMID 31498409

   The official account of the 2019 Preamble: evidence definitions, the integration table, the end of Group 4 and conflict-of-interest rules. The first author disclosed plaintiff-side expert-witness work in US talc litigation.

5. 5
   Krewski D, Bird M, Al-Zoughool M, et al. Key characteristics of 86 agents known to cause cancer in humans.J Toxicol Environ Health B Crit Rev · 2019 · 22(7-8):244-263doi:10.1080/10937404.2019.1643536 · PMID 31637961

   Counts more than 1,000 agents evaluated and 120 in Group 1 through Volume 119, and finds an average of four key characteristics per Group 1 agent; two authors are at Risk Sciences International, a commercial consultancy.

6. 6
   Krewski D, Rice JM, Bird M, et al. Concordance between sites of tumor development in humans and in experimental animals for 111 agents that are carcinogenic to humans.J Toxicol Environ Health B Crit Rev · 2019 · 22(7-8):203-236doi:10.1080/10937404.2019.1642586 · PMID 31795923

   Dates Volume 100 (compiled 2008-2009, published 2012, covering the 107 Group 1 agents of 2009) and shows 87% organ-system concordance between human and animal tumors where both exist; some authors hold consulting affiliations.

7. 7
   Berrington de González A, Masten SA, Bhatti P, et al. Advisory Group recommendations on priorities for the IARC Monographs.Lancet Oncol · 2024 · 25(5):546-548doi:10.1016/S1470-2045(24)00208-0 · PMID 38621402

   The March 2024 Advisory Group (28 scientists, 22 countries, more than 200 nominations) that set priorities for 2025-2029 and noted the backlog of pesticides and infectious agents.

8. 8
   Schubauer-Berigan MK, Madia F, Kunzmann AT, et al. Progress in identifying the preventable causes of human cancer: the experience of the IARC Monographs program.J Natl Cancer Inst Monogr · 2026 · 2026(72):78-85doi:10.1093/jncimonographs/lgaf039 · PMID 42008728

   IARC's own 2026 survey of the 135 Group 1 agents and the 24 added since Volume 100; written by Monographs staff.

9. 9
   Rumgay H, Georges D, Huang Y, et al. Global burden of cancer attributable to infections in 2024: a worldwide incidence analysis.Lancet Oncol · 2026 · 27(10):1237-1248doi:10.1016/S1470-2045(26)00307-4 · PMID 42805198

   IARC's current count of infection-attributable cancers and its list of Group 1 infectious agents; estimates without uncertainty intervals, built on thin registry coverage in Africa.

10. 10
    Karagas MR, Kaldor J, Michaelis M, et al. Carcinogenicity of hepatitis D virus, human cytomegalovirus, and Merkel cell polyomavirus.Lancet Oncol · 2025 · published online 26 June 2025doi:10.1016/S1470-2045(25)00403-6 · PMID 40587985

    Volume 139 (June 2025): hepatitis D virus and Merkel cell polyomavirus to Group 1, cytomegalovirus 2B, with a recorded minority view; it followed the Advisory Group's note that no infectious agent had been evaluated since 2012.

11. 11
    Lauby-Secretan B, Scoccianti C, Loomis D, et al. Body Fatness and Cancer--Viewpoint of the IARC Working Group.N Engl J Med · 2016 · 375(8):794-8doi:10.1056/NEJMsr1606602 · PMID 27557308

    Handbooks Volume 16 (2016): avoiding excess body fat lowers the risk of 13 cancers; based mostly on observational studies of excess fat rather than trials of weight loss.

12. 12
    Baan RA, Straif K. The Monographs Programme of the International Agency for Research on Cancer. A brief history of its Preamble.ALTEX · 2022 · 39(3):443-450doi:10.14573/altex.2004081 · PMID 34164695

    Two retired Monographs staff trace the Preamble from the late 1970s to 2019; confirms evaluations can now proceed without animal data, which is not the same as mechanisms alone reaching Group 1.

13. 13
    Buisson Y. [Control of Opisthorchis viverrini infection for cholangiocarcinoma prevention].Bull Soc Pathol Exot · 2017 · 110(1):61-67doi:10.1007/s13149-017-0544-8 · PMID 28105582

    French review dating O. viverrini's Group 1 rating to 1994 and C. sinensis's to 2009, and explaining why mass deworming fails against reinfection.

14. 14
    Boobis AR, Cohen SM, Dellarco VL, et al. Classification schemes for carcinogenicity based on hazard-identification have become outmoded and serve neither science nor society.Regul Toxicol Pharmacol · 2016 · 82:158-166doi:10.1016/j.yrtph.2016.10.014 · PMID 27780763

    The strongest statement of the hazard-only critique and the source of the processed-meat and mustard-gas comparison; one author is at Syngenta, a pesticide maker, and several are consultants.

15. 15
    Gapstur SM, Mariosa D, Neamtiu L, et al. The IARC Perspective on the Effects of Policies on Reducing Alcohol Consumption.N Engl J Med · 2025 · 392(17):1752-1759doi:10.1056/NEJMsr2413289 · PMID 40305721

    Handbooks Volume 20B (2025): which alcohol policies reduce drinking; evidence mostly from high-income countries and from before online sales.

16. 16
    Mignogna MD, Fedele S, Lo Russo L. The World Cancer Report and the burden of oral cancer.Eur J Cancer Prev · 2004 · 13(2):139-42doi:10.1097/00008469-200404000-00008 · PMID 15100581

    Commentary on the first World Cancer Report and its projection from 10 million new cases in 2000 to 15 million in 2020.

17. 17
    McGuire S. World Cancer Report 2014. Geneva, Switzerland: World Health Organization, International Agency for Research on Cancer, WHO Press, 2015.Adv Nutr · 2016 · 7(2):418-9doi:10.3945/an.116.012211 · PMID 26980827

    Notice of the 2014 edition of the World Cancer Report; cited for the edition's existence and publisher.

18. 18
    Portier CJ, Armstrong BK, Baguley BC, et al. Differences in the carcinogenic evaluation of glyphosate between the International Agency for Research on Cancer (IARC) and the European Food Safety Authority (EFSA).J Epidemiol Community Health · 2016 · 70(8):741-5doi:10.1136/jech-2015-207005 · PMID 26941213

    Scientists supporting IARC's 2A call set out the basis of the rating and criticize the EU's reliance on unpublished industry studies; an advocacy response, not an independent re-analysis. Lead author Christopher Portier attended the 2015 glyphosate meeting as an invited specialist and later consulted for plaintiffs in the Roundup litigation.

19. 19
    Shin HR, Oh JK, Lim MK, et al. Descriptive epidemiology of cholangiocarcinoma and clonorchiasis in Korea.J Korean Med Sci · 2010 · 25(7):1011-6doi:10.3346/jkms.2010.25.7.1011 · PMID 20592891

    Dates C. sinensis's Group 1 rating to 2009 and estimates about 10% of Korean cholangiocarcinomas attributable to it; lead author was at IARC.

20. 20
    Zahm S, Bonde JP, Chiu WA, et al. Carcinogenicity of perfluorooctanoic acid and perfluorooctanesulfonic acid.Lancet Oncol · 2024 · 25(1):16-17doi:10.1016/S1470-2045(23)00622-8 · PMID 38043561

    Volume 135: PFOA to Group 1 on animal plus mechanistic evidence in exposed people, PFOS to 2B on mechanistic evidence alone; the clearest worked example of the 2019 rules.

21. 21
    Saracci R, Wild CP. International Agency for Research on Cancer: The First 50 Years, 1965-2015. Lyon: IARC; 2015.IARC · 2015publications.iarc.who.int/Non-Series-Publications/The-History-Of-Iarc/International-Agency-For-Research-On-Cancer-The-First-50-Years-1965%E2%80%932015

    IARC's official institutional history; cited for the 1965 founding, the choice of Lyon and the succession of directors. Not indexed in PubMed; free to read on the IARC publications site.

22. 22
    Saracci R, Vineis P. Environment and cancer: the legacy of Lorenzo Tomatis.Environ Health · 2011 · 10 Suppl 1:S1doi:10.1186/1476-069X-10-S1-S1 · PMID 21489205

    Credits Tomatis with founding the Monographs (dated here to 1972) and gives his directorship, 1982 to 1993; also warns that attributable fractions are population-specific pointers, not precise measurements.

23. 23
    Weiderpass E, Chajès V, Chauvet C, et al. Bridging science and action: celebrating 60 years of the IARC and looking ahead.J Natl Cancer Inst Monogr · 2026 · 2026(72):1-2doi:10.1093/jncimonographs/lgag002 · PMID 42008723

    IARC's 60th-anniversary editorial, by the Director and staff; cited for the agency's history and current leadership.

24. 24
    IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Schistosomes, liver flukes and Helicobacter pylori.IARC Monogr Eval Carcinog Risks Hum · 1994 · 61:1-241PMID 7715068

    Volume 61, from the Working Group that met in Lyon on 7-14 June 1994; the primary record for every 1994 parasite rating.

25. 25
    IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Biological agents.IARC Monogr Eval Carcinog Risks Hum · 2012 · 100(Pt B):1-441PMID 23189750

    Volume 100B, A review of human carcinogens: the biological Group 1 agents, including the three Group 1 flukes. It re-reviewed the agents then in Group 1 and also re-evaluated Clonorchis sinensis, raising it from Group 2A (1994) to Group 1; it did not re-evaluate S. japonicum, S. mansoni or O. felineus.

26. 26
    Bouvard V, Baan R, Straif K, et al. A review of human carcinogens--Part B: biological agents.Lancet Oncol · 2009 · 10(4):321-2doi:10.1016/s1470-2045(09)70096-8 · PMID 19350698

    The April 2009 announcement of the Volume 100B conclusions by IARC staff, three years before the book; explains why the same decisions carry the dates 2009 and 2012.

27. 27
    Stayner LT, Carreón-Valencia T, Demers PA, et al. Carcinogenicity of talc and acrylonitrile.Lancet Oncol · 2024 · 25(8):962-963doi:10.1016/S1470-2045(24)00384-X · PMID 38976996

    Volume 136 (June 2024): acrylonitrile Group 1, talc 2A, with the Working Group's own caveats on recall bias and asbestos contamination.

28. 28
    Loomis D, Guyton KZ, Grosse Y, et al. Carcinogenicity of drinking coffee, mate, and very hot beverages.Lancet Oncol · 2016 · 17(7):877-8doi:10.1016/S1470-2045(16)30239-X · PMID 27318851

    The 2016 reversal that moved coffee from Group 2B down to Group 3 and rated very hot beverages Group 2A; IARC staff.

29. 29
    Berry A, Iriart X, Fillaux J, Magnaval JF. [Urinary schistosomiasis and cancer].Bull Soc Pathol Exot · 2017 · 110(1):68-75doi:10.1007/s13149-017-0547-4 · PMID 28185084

    French review of the century-long case linking S. haematobium to bladder cancer, and of the absence of firm evidence for S. mansoni and S. japonicum.

30. 30
    Sripa B, Kaewkes S, Sithithaworn P, et al. Liver fluke induces cholangiocarcinoma.PLoS Med · 2007 · 4(7):e201doi:10.1371/journal.pmed.0040201 · PMID 17622191

    Review of O. viverrini epidemiology and pathogenesis, including the hamster finding that the fluke needs a nitrosamine co-exposure to produce cancer reliably; also records that C. sinensis was not yet in Group 1 in 2007.

31. 31
    Baan R, Grosse Y, Lauby-Secretan B, et al. Carcinogenicity of radiofrequency electromagnetic fields.Lancet Oncol · 2011 · 12(7):624-6doi:10.1016/s1470-2045(11)70147-4 · PMID 21845765

    The 2011 announcement of the radiofrequency evaluation by IARC staff; no abstract in the record.

32. 32
    L'Abbate N. [Motivation and significance of IARC classification for mobile phone].G Ital Med Lav Ergon · 2011 · 33(3 Suppl):384-7PMID 23393882

    Italian summary of the evidence the 2011 Working Group weighed and of its limited-evidence finding for glioma and acoustic neuroma.

33. 33
    Smith MT, Guyton KZ, Gibbons CF, et al. Key Characteristics of Carcinogens as a Basis for Organizing Data on Mechanisms of Carcinogenesis.Environ Health Perspect · 2016 · 124(6):713-21doi:10.1289/ehp.1509912 · PMID 26600562

    The paper that defined the ten key characteristics now used to organize mechanistic evidence; a framework for sorting studies, not a test that decides a classification by itself.

34. 34
    DeMarini DM. Origin Story of IARC's 10 Key Characteristics of Carcinogens.Environ Mol Mutagen · 2025 · 66(8):404-411doi:10.1002/em.70028 · PMID 40817717

    Dates the key characteristics to two IARC workshops held in April and November 2012, after the Volume 100 review, and published in 2015-2016.

35. 35
    Guyton KZ, Loomis D, Grosse Y, et al. Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate.Lancet Oncol · 2015 · 16(5):490-1doi:10.1016/S1470-2045(15)70134-8 · PMID 25801782

    The March 2015 announcement of Volume 112 by IARC staff; the record has no abstract, so the evidence behind the 2A rating is taken from later papers that quote it.

36. 36
    Weisenburger DD. An Update of Evidence that the Herbicide Glyphosate (Roundup) is a Cause of Non-Hodgkin Lymphoma.Clin Lymphoma Myeloma Leuk · 2026 · 26(3):178-183doi:10.1016/j.clml.2025.11.005 · PMID 41318253

    Single-author narrative review arguing the evidence has strengthened since 2015 and noting that most regulators have not followed IARC; a review, not new data. The author, Dennis Weisenburger, has served as a plaintiffs' expert witness in US Roundup litigation and co-signed the defenses of IARC cited here [3][26].

37. 37
    Bouvard V, Loomis D, Guyton KZ, et al. Carcinogenicity of consumption of red and processed meat.Lancet Oncol · 2015 · 16(16):1599-600doi:10.1016/S1470-2045(15)00444-1 · PMID 26514947

    The October 2015 announcement of the meat evaluations by IARC staff; no abstract in the record.

38. 38
    Domingo JL, Nadal M. Carcinogenicity of consumption of red meat and processed meat: A review of scientific news since the IARC decision.Food Chem Toxicol · 2017 · 105:256-261doi:10.1016/j.fct.2017.04.028 · PMID 28450127

    Independent review giving the meat classifications in IARC's words and listing the open questions on mechanism, cooking and white meat.

39. 39
    Andreotti G, Koutros S, Hofmann JN, et al. Glyphosate Use and Cancer Incidence in the Agricultural Health Study.J Natl Cancer Inst · 2018 · 110(5):509-516doi:10.1093/jnci/djx233 · PMID 29136183

    The largest prospective cohort: no association with non-Hodgkin lymphoma among 54,251 applicators, a non-significant acute myeloid leukemia signal; self-reported exposure.

40. 40
    Riboli E, Beland FA, Lachenmeier DW, et al. Carcinogenicity of aspartame, methyleugenol, and isoeugenol.Lancet Oncol · 2023 · 24(8):848-850doi:10.1016/S1470-2045(23)00341-8 · PMID 37454664

    A French cohort of 102,865 adults with repeated 24-hour dietary records, one of the studies the 2023 panel weighed, and not the largest aspartame cohort: the NIH-AARP Diet and Health Study analyzed aspartame in 473,984 adults (Lim U, Subar AF, Mouw T, et al. Cancer Epidemiol Biomarkers Prev 2006;15(9):1654-9; PMID 16985027; doi 10.1158/1055-9965.EPI-06-0203). It found small relative increases with lower bounds near 1, which its authors say may reflect bias, confounding or reverse causality.

41. 41
    Goodman JE, Boon DN, Jack MM. Perspectives on recent reviews of aspartame cancer epidemiology.Glob Epidemiol · 2023 · 6:100117doi:10.1016/j.gloepi.2023.100117 · PMID 37637718

    Sets the IARC and JECFA aspartame conclusions side by side and argues for Group 3; authors are at Gradient and the American Beverage Association.

42. 42
    DeMarini DM, Gwinn W, Watkins E, et al. IARC Workshop on the Key Characteristics of Carcinogens: Assessment of End Points for Evaluating Mechanistic Evidence of Carcinogenic Hazards.Environ Health Perspect · 2025 · 133(2):25001doi:10.1289/EHP15389 · PMID 39899356

    Report of the 2023 IARC workshop that agreed which endpoints count as evidence for each key characteristic.

43. 43
    Goodman JE, Drury NL, Marchitti SA. Comment on “IARC Workshop on the Key Characteristics of Carcinogens...”Environ Health Perspect · 2025doi:10.1289/EHP17383 · PMID 40168618

    Gradient consultants' criticism of the 2023 key-characteristics workshop report.

44. 44
    Baan R, Straif K, Grosse Y, et al. Carcinogenicity of carbon black, titanium dioxide, and talc.Lancet Oncol · 2006 · 7(4):295-6doi:10.1016/s1470-2045(06)70651-9 · PMID 16598890

    The 2006 talc evaluation: Group 2B for perineal use of talc-based body powder and Group 3 for talc not containing asbestos, the ratings superseded in 2024.

45. 45
    IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Re-evaluation of some organic chemicals, hydrazine and hydrogen peroxide.IARC Monogr Eval Carcinog Risks Hum · 1999 · 71:1-1554PMID 10507919

    Volume 71, the 1999 re-evaluation that placed acrylonitrile in Group 2B before its 2024 move to Group 1.

46. 46
    Karipidis K, Baaken D, Loney T, et al. The effect of exposure to radiofrequency fields on cancer risk in the general and working population: A systematic review of human observational studies - Part I: Most researched outcomes.Environ Int · 2024 · 191:108983doi:10.1016/j.envint.2024.108983 · PMID 39241333

    WHO-commissioned systematic review finding moderate-certainty evidence of no increase in brain and head tumors from mobile phones; observational data, partly funded by WHO and national radiation agencies.

47. 47
    Mevissen M, Ducray A, Ward JM, et al. Effects of radiofrequency electromagnetic field exposure on cancer in laboratory animal studies, a systematic review.Environ Int · 2025 · 199:109482doi:10.1016/j.envint.2025.109482 · PMID 40339346

    WHO-commissioned animal review finding high certainty for gliomas and heart schwannomas in male rats; corrigendum Environ Int 2026;214:110368, PMID 42442967.

48. 48
    IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Hepatitis viruses.IARC Monogr Eval Carcinog Risks Hum · 1994 · 59:1-255PMID 7933461

    Volume 59, which first evaluated hepatitis D virus and placed it in Group 3 before its 2025 move to Group 1.

49. 49
    IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Malaria and some polyomaviruses (SV40, BK, JC, and Merkel cell viruses).IARC Monogr Eval Carcinog Risks Hum · 2014 · 104:9-350PMID 26173303

    Volume 104: the full review behind the 2012 malaria (Group 2A) and Merkel cell polyomavirus (Group 2A) evaluations.

50. 50
    Williams GM, Kroes R, Munro IC. Retraction notice to "Safety evaluation and risk assessment of the herbicide roundup and its active ingredient, glyphosate, for humans" [Regul. Toxicol. Pharm. 31 (2000) 117-165].Regul Toxicol Pharmacol · 2025 · 106006doi:10.1016/j.yrtph.2025.106006 · PMID 41428335

    The December 2025 retraction notice for the 2000 Roundup safety review. The retraction cited possible ghostwriting, undisclosed conflicts of interest and omission of unpublished studies; in 2026 a group of toxicologists disputed it and called for its reversal [74].

51. 51
    Lachenmeier DW, Arrandale VH, DeMarini DM, et al. Carcinogenicity of tris(chloropropyl) phosphate, butyraldehyde, and cumyl hydroperoxide.Lancet Oncol · 2026 · published online 27 March 2026doi:10.1016/S1470-2045(26)00168-3 · PMID 41911935

    Volume 141 (March 2026): TCPP to Group 2A on sufficient animal evidence and strong mechanistic evidence in human primary cells, with inadequate human evidence.

52. 52
    [No authors listed]. Advisory Group recommendations on priorities for the IARC Monographs.Lancet Oncol · 2019 · 20(6):763-764doi:10.1016/S1470-2045(19)30246-3 · PMID 31005580

    The previous five-year priority round, for 2020-2024; the record has no abstract and is cited for the existence and timing of that round.

53. 53
    International Agency for Research on Cancer. Preamble to the IARC Monographs (amended January 2019). Lyon: IARC; 2019.IARC · 2019monographs.iarc.who.int/wp-content/uploads/2019/07/Preamble-2019.pdf

    IARC's standing rulebook: defines invited specialists as experts with a conflict of interest who take part without drafting the evaluation or voting, and sets out the public call for experts before each meeting.

54. 54
    Goodman JE, Mayfield DB, Becker RA, Hartigan SB, Erraguntla NK. Recommendations for further revisions to improve the International Agency for Research on Cancer (IARC) Monograph program.Regul Toxicol Pharmacol · 2020 · 113:104639doi:10.1016/j.yrtph.2020.104639 · PMID 32147291

    Calls the 2019 Preamble an improvement but faults its lack of standardized methods and of outside peer review; three authors are American Chemistry Council staff and two are at the consultancy Gradient.

55. 55
    Cattley RC, De Roos AJ, Mandrioli D, et al. Carcinogenicity of atrazine, alachlor, and vinclozolin.Lancet Oncol · 2025 · published online 21 November 2025doi:10.1016/S1470-2045(25)00702-8 · PMID 41285132

    Volume 140 (October-November 2025): atrazine and alachlor 2A, vinclozolin 2B, a clean illustration of how human, animal and mechanistic findings combine.

56. 56
    Drury NL, Prueitt RL, Beck BD. Commentary: Understanding IARC's PFOA and PFOS carcinogenicity assessments.Regul Toxicol Pharmacol · 2024 · 154:105726doi:10.1016/j.yrtph.2024.105726 · PMID 39433235

    Gradient consultants arguing the PFOA and PFOS evidence was overstated and the key characteristics used as a checklist.

57. 57
    Leija-Montoya AG, González-Ramírez J, Martínez-Coronilla G, et al. Roles of microRNAs and Long Non-Coding RNAs Encoded by Parasitic Helminths in Human Carcinogenesis.Int J Mol Sci · 2022 · 23(15):8173doi:10.3390/ijms23158173 · PMID 35897749

    Review giving S. japonicum's Group 2B rating; it also still describes four IARC groups including the retired Group 4, three years after the change.

58. 58
    Jain S. Exploring the potential role of Opisthorchis felineus infection in cholangiocarcinogenesis.Mol Biochem Parasitol · 2026 · 266:111733doi:10.1016/j.molbiopara.2026.111733 · PMID 41587590

    Single-author 2026 review stating O. felineus's current Group 3 rating and arguing for reclassification; an advocacy position, not a new study.

59. 59
    Haile D, Harding KL, McLaughlin SA, et al. Health effects associated with consumption of processed meat, sugar-sweetened beverages and trans fatty acids: a Burden of Proof study.Nat Med · 2025 · 31(7):2244-2254doi:10.1038/s41591-025-03775-8 · PMID 40588677

    Estimates at least a 7% average increase in colorectal-cancer risk from processed meat and rates the evidence two stars out of five (weak or inconsistent).

60. 60
    Pesch B, Kendzia B, Gustavsson P, et al. Cigarette smoking and lung cancer--relative risk estimates for the major histological types from a pooled analysis of case-control studies.Int J Cancer · 2012 · 131(5):1210-9doi:10.1002/ijc.27339 · PMID 22052329

    Pooled analysis of 13,169 lung-cancer cases: men smoking more than 30 cigarettes a day had odds ratios of about 22 to 111 versus never-smokers, depending on tumor type; a worked contrast for hazard versus magnitude.

61. 61
    Tarazona JV, Court-Marques D, Tiramani M, et al. Glyphosate toxicity and carcinogenicity: a review of the scientific basis of the European Union assessment and its differences with IARC.Arch Toxicol · 2017 · 91(8):2723-2743doi:10.1007/s00204-017-1962-5 · PMID 28374158

    European Food Safety Authority and German risk-assessment staff explain why the EU, using additional data, found no carcinogenic hazard; the regulator's own defense.

62. 62
    Gapstur SM, Bouvard V, Nethan ST, et al. The IARC Perspective on Alcohol Reduction or Cessation and Cancer Risk.N Engl J Med · 2023 · 389(26):2486-2494doi:10.1056/NEJMsr2306723 · PMID 38157507

    Handbooks Volume 20A (2023), on whether reducing or stopping drinking lowers cancer risk; the record carries no abstract.

63. 63
    Park JY, Lee YC, Moayyedi P, et al. Screen-and-Treat Programs for Gastric Cancer Prevention - IARC Working Group Report.N Engl J Med · 2026 · 394(11):1131-1137doi:10.1056/NEJMsb2515372 · PMID 41812202

    2026 IARC Working Group report on testing for and treating H. pylori to prevent stomach cancer; cited for the topic, as the record carries no abstract.

64. 64
    Neamtiu L, Callister MEJ, Crosbie P, et al. IARC Perspective on Lung Cancer Screening.N Engl J Med · 2026 · published online 24 September 2026doi:10.1056/NEJMsb2608211 · PMID 42788692

    2026 IARC perspective on lung-cancer screening; cited for the topic, as the record carries no abstract.

65. 65
    Autier P, Jørgensen KJ, Støvring H. Evaluation of screening mammography effectiveness: The IARC recommendations of 2015 need revision.Eur J Cancer · 2025 · 227:115657doi:10.1016/j.ejca.2025.115657 · PMID 40712255

    Systematic review arguing that the 2015 IARC breast-screening evaluation mistook self-selection for benefit; a critique of a Handbook, not of a Monograph.

66. 66
    Lauby-Secretan B. Response to the current perspective: Evaluation of screening mammography effectiveness: The IARC recommendations of 2015 need revision.Eur J Cancer · 2025 · 226:115658doi:10.1016/j.ejca.2025.115658 · PMID 40729841

    IARC's Handbooks lead replying to the 2025 mammography critique in the same journal.

67. 67
    Giorgi Rossi P, Venturelli F. Letter Re: Evaluation of screening mammography effectiveness... different perspectives and questions require different approaches.Eur J Cancer · 2025 · 227:115659doi:10.1016/j.ejca.2025.115659 · PMID 40712256

    Screening researchers' reply to the 2025 mammography critique.

68. 68
    Portier CJ. A comprehensive analysis of the animal carcinogenicity data for glyphosate from chronic exposure rodent carcinogenicity studies.Environ Health · 2020 · 19(1):18doi:10.1186/s12940-020-00574-1 · PMID 32050978

    Re-analysis of rodent studies by Christopher Portier, an invited specialist at the 2015 IARC glyphosate meeting who later consulted for plaintiffs in the Roundup litigation.

69. 69
    Debras C, Chazelas E, Srour B, et al. Artificial sweeteners and cancer risk: Results from the NutriNet-Santé population-based cohort study.PLoS Med · 2022 · 19(3):e1003950doi:10.1371/journal.pmed.1003950 · PMID 35324894

    The largest aspartame cohort available in 2023: small relative increases with lower bounds near 1, which its authors say may reflect bias, confounding or reverse causality.

70. 70
    European Food Safety Authority. Conclusion on the peer review of the pesticide risk assessment of the active substance glyphosate.EFSA J · 2015 · 13(11):4302doi:10.2903/j.efsa.2015.4302 · PMID 42169844

    EFSA's November 2015 conclusion that glyphosate is unlikely to pose a carcinogenic hazard; the regulators' position.

71. 71
    European Food Safety Authority (EFSA), Álvarez F, Arena M, et al. Peer review of the pesticide risk assessment of the active substance glyphosate.EFSA J · 2023 · 21(7):e08164doi:10.2903/j.efsa.2023.8164 · PMID 37502013

    EFSA's July 2023 re-review, finding no critical area of concern; preceded the EU's ten-year renewal of glyphosate in November 2023.

72. 72
    Zhang L, Rana I, Shaffer RM, Taioli E, Sheppard L. Exposure to glyphosate-based herbicides and risk for non-Hodgkin lymphoma: A meta-analysis and supporting evidence.Mutat Res Rev Mutat Res · 2019 · 781:186-206doi:10.1016/j.mrrev.2019.02.001 · PMID 31342895

    Meta-analysis of the highest-exposure groups: meta-relative risk 1.41 for non-Hodgkin lymphoma; an observational association, and the lead author later served on the 2023 aspartame Working Group (Volume 134) [36].

73. 73
    Krimsky S, Gillam C. Roundup litigation discovery documents: implications for public health and journal ethics.J Public Health Policy · 2018 · 39(3):318-326doi:10.1057/s41271-018-0134-z · PMID 29884897

    Review of court-released Monsanto documents reporting ghostwriting and interference; one author is at U.S. Right to Know, an advocacy group.

74. 74
    Borgert CJ, Abdollahi M, Ansell JM, et al. Retraction of the landmark glyphosate safety publication by Williams, Kroes and Munro (2000) should be reversed.EXCLI J · 2026 · 25:1107-1116doi:10.17179/excli2026-9644 · PMID 42517087

    A 2026 letter by toxicologists, several from consultancies and industry, calling the retraction editorial overreach and asking for its reversal.

75. 75
    Reddick R. Glyphosate: US Supreme Court ruling could block lawsuits alleging pesticide causes cancer.BMJ · 2026 · 393:s859doi:10.1136/bmj.s859 · PMID 42086304

    May 2026 news report that a US Supreme Court ruling could block state lawsuits faulting Roundup for lacking a cancer warning.

76. 76
    Liang L. Glyphosate: US Supreme Court backs Trump stance, angering MAHA.BMJ · 2026 · 394:e100128doi:10.1136/bmj-2026-100128 · PMID 42386271

    July 2026 news report that the US Supreme Court sided with the federal government's position in the Roundup labeling case.

77. 77
    Panzacchi S, Tibaldi E, De Angelis L, et al. Carcinogenic effects of long-term exposure from prenatal life to glyphosate and glyphosate-based herbicides in Sprague-Dawley rats.Environ Health · 2025 · 24(1):36doi:10.1186/s12940-025-01187-2 · PMID 40490737

    The Ramazzini Institute's 2025 lifetime rat study reporting tumors at many sites at doses including the EU acceptable daily intake; one laboratory's study, not yet assessed by regulators.

78. 78
    Johnston BC, Zeraatkar D, Han MA, et al. Unprocessed Red Meat and Processed Meat Consumption: Dietary Guideline Recommendations From the Nutritional Recommendations (NutriRECS) Consortium.Ann Intern Med · 2019 · 171(10):756-764doi:10.7326/M19-1621 · PMID 31569235

    The guideline that told adults they could continue current meat intake on low-certainty evidence; the article was later corrected, and it judges certainty of benefit, not hazard.

79. 79
    Melnick RL, Moskowitz JM, Héroux P, et al. The WHO-commissioned systematic reviews on health effects of radiofrequency radiation provide no assurance of safety.Environ Health · 2025 · 24(1):70doi:10.1186/s12940-025-01220-4 · PMID 41034851

    Advocacy group (ICBE-EMF) arguing the WHO reviews do not prove safety and that the rat-tumor findings support lower exposure limits.

80. 80
    Landrigan PJ, Straif K, Birnbaum LS, et al. Irregularities in the IARC Working Group Evaluation of Ramazzini Institute Aspartame Studies.Ann Glob Health · 2025 · 91(1):28doi:10.5334/aogh.4771 · PMID 40487707

    Ramazzini Institute advisers, including former Monographs head Kurt Straif, arguing the aspartame animal evidence should have been judged sufficient and the rating higher.

81. 81
    Romanos-Nanclares A, Schernhammer E, Willett WC, Holmes MD, Chen WY, Eliassen AH. Consumption of aspartame and risk of breast cancer in the Nurses' Health Studies.J Natl Cancer Inst · 2025 · 117(4):795-800doi:10.1093/jnci/djae259 · PMID 39418201

    About 30 years of follow-up found no association between aspartame and breast cancer (hazard ratio 1.00 per 200 mg a day).

82. 82
    Zhu X, Welsh JA, McCullough ML, et al. Association between Aspartame Consumption and Cancer Risk: Evidence from a Large Prospective Cohort.J Nutr · 2026 · 156(5):101460doi:10.1016/j.tjnut.2026.101460 · PMID 41765137

    In 100,004 older US adults, aspartame consumers had a 13% higher overall cancer risk but no dose-response, which the authors say calls for cautious interpretation.

83. 83
    Goodman JE, Boon DN. Interpretation of the IARC quantitative bias analysis of talc and ovarian cancer.Glob Epidemiol · 2026 · 11:100251doi:10.1016/j.gloepi.2026.100251 · PMID 41658396

    Argues the talc Working Group's own bias analysis undercuts its conclusion; authors are at the consultancy Gradient, and the record does not state funding.

84. 84
    Korchevskiy AA, Wylie AG. Particles, fragments, fibers: what IARC missed in its assessment of talc mineralogy (Authors' reply).Crit Rev Toxicol · 2026 · 56(1):48-56doi:10.1080/10408444.2026.2641747 · PMID 41920094

    Argues Volume 136's mineralogical definitions of asbestos and asbestiform talc ignore recent science and blur talc from asbestos contamination.

85. 85
    Gualtieri AF. Comments on the article “The IARC re-classification of talc carcinogenicity: a move in the wrong direction?” by A.A. Korchevskiy and A.G. Wylie (2025).Crit Rev Toxicol · 2026 · 56(1):38-47doi:10.1080/10408444.2026.2641755 · PMID 41919990

    A talc Working Group member's rebuttal of the Korchevskiy and Wylie mineralogy critique.

86. 86
    Infante PF, Melnick R, Vainio H, Huff J. Commentary: IARC Monographs Program and public health under siege by corporate interests.Am J Ind Med · 2018 · 61(4):277-281doi:10.1002/ajim.22811 · PMID 29397007

    Describes a campaign by economic interests, including US congressional intervention, to discredit IARC after the glyphosate and meat decisions; a defense of IARC.

87. 87
    Tarone RE. Conflicts of interest, bias, and the IARC Monographs Program.Regul Toxicol Pharmacol · 2018 · 98:A1-A4doi:10.1016/j.yrtph.2018.09.005 · PMID 30194952

    Argues that conflicts of interest and bias within the Monographs program itself, illustrated by glyphosate, deserve scrutiny; the critics' counter-case.

88. 88
    Pira E, De Piano ML, Declementi M, Godono A, Longo D. Congress of the United States, Ramazzini Institute and its affiliates, IARC: questions on scientific transparency.G Ital Med Lav Ergon · 2019 · 41(3):253-254PMID 31242355

    Short Italian commentary on transparency questions raised in the US Congress; the record has no abstract and is cited only for what its title states.

89. 89
    McCormack V, Simba H, Abnet CC, et al. The continuing importance of the IARC's international remit in cancer research.J Natl Cancer Inst Monogr · 2026 · 2026(72):95-101doi:10.1093/jncimonographs/lgaf042 · PMID 42008730

    IARC scientists and partners on trust and independence amid vested interests; an institutional perspective. Correction published 1 September 2026: J Natl Cancer Inst Monogr, doi 10.1093/jncimonographs/lgag018, PMID 42679314.

90. 90
    Paluch M, Cudzik M, Kędra A, et al. Can flukes cause cancer? Insight into molecular links between parasites and carcinogenesis.Mol Biochem Parasitol · 2025 · 264:111707doi:10.1016/j.molbiopara.2025.111707 · PMID 41138780

    2025 review naming the six flukes listed by IARC; it does not itself give each species' group.

91. 91
    Bouvard V, Baan RA, Grosse Y, et al. Carcinogenicity of malaria and of some polyomaviruses.Lancet Oncol · 2012 · 13(4):339-40doi:10.1016/s1470-2045(12)70125-0 · PMID 22577663

    The 2012 announcement (Volume 104) placing the malaria parasite Plasmodium falciparum in Group 2A for Burkitt lymphoma; the last parasite IARC has evaluated.

92. 92
    von Bülow V, Lichtenberger J, Grevelding CG, Falcone FH, Roeb E, Roderfeld M. Does Schistosoma mansoni Facilitate Carcinogenesis?Cells · 2021 · 10(8):1982doi:10.3390/cells10081982 · PMID 34440754

    Review stating S. mansoni's Group 3 rating and summarizing case reports, animal and cell data; the PubMed title drops the italicized species name.

93. 93
    Gouveia MJ, Santos J, Brindley PJ, et al. Estrogen-like metabolites and DNA-adducts in urogenital schistosomiasis-associated bladder cancer.Cancer Lett · 2015 · 359(2):226-32doi:10.1016/j.canlet.2015.01.018 · PMID 25615421

    Mechanistic evidence measured in 40 Angolan patients: estrogen-derived DNA adducts and oxidative-damage products in urine; small and without a control group of healthy local residents.

94. 94
    Huang YL, Zhang KY, Sun YL, Qian MB, Wang Z. The risk of hepatobiliary complications in Clonorchis and Opisthorchis infection: A systematic review and meta-analysis.Acta Trop · 2024 · 260:107457doi:10.1016/j.actatropica.2024.107457 · PMID 39521195

    The largest pooled analysis of liver flukes and cholangiocarcinoma, with species-specific odds ratios for C. sinensis and O. viverrini but none for O. felineus.

95. 95
    Homsana A, Southisavath P, Kling K, et al. Burden and risk factors of suspected cholangiocarcinoma in high Opisthorchis viverrini endemic rural communities in southern Lao PDR.PLoS Negl Trop Dis · 2024 · 18(11):e0012617doi:10.1371/journal.pntd.0012617 · PMID 39602377

    Cross-sectional ultrasound survey of 3,400 Lao villagers; the endpoint is suspected, not confirmed, cholangiocarcinoma.

96. 96
    Jain S. Can Schistosoma japonicum infection cause liver cancer?J Helminthol · 2025 · 99:e11doi:10.1017/S0022149X24000762 · PMID 39924660

    A 2025 review stating S. japonicum's Group 2B rating and noting co-infection with hepatitis viruses as a complicating factor.

97. 97
    Shousha HI, Abdelaziz AO, Nabeel MM, et al. Schistosoma mansoni infection and the occurrence, characteristics, and survival of patients with hepatocellular carcinoma: an observational study over a decade.Pathog Glob Health · 2022 · 116(2):119-127doi:10.1080/20477724.2021.1975081 · PMID 34494507

    Egyptian clinic study of 1,446 liver-cancer patients; a modest adjusted association in a population treated for hepatitis C, which limits causal reading. The PubMed title drops the italicized species name.

98. 98
    Fedorova OS, Kovshirina YV, Kovshirina AE, et al. Opisthorchis felineus infection and cholangiocarcinoma in the Russian Federation: A review of medical statistics.Parasitol Int · 2017 · 66(4):365-371doi:10.1016/j.parint.2016.07.010 · PMID 27474689

    Ecological comparison across 83 Russian regions finding no significant correlation between O. felineus and liver or bile-duct cancer; the weakest study design, so weak evidence of absence.

99. 99
    Ramírez AT, Clifford GM, Dillner J, et al. Reflections Regarding Validation of New HPV Tests With Reduced HPV Genotypes: Report From an IARC Expert Consultation.J Med Virol · 2025 · 97(3):e70310doi:10.1002/jmv.70310 · PMID 40109087

    IARC expert consultation stating that 12 HPV genotypes are Group 1 and that eight types (16, 18, 31, 33, 35, 45, 52, 58) cause about 95% of cervical cancers.

100. 100
     Lishai EA, Zaparina OG, Kapushchak YK, et al. Comparative liver transcriptome analysis in hamsters infected with food-borne trematodes Opisthorchis felineus, Opisthorchis viverrini, or Clonorchis sinensis.PLoS Negl Trop Dis · 2024 · 18(12):e0012685doi:10.1371/journal.pntd.0012685 · PMID 39652576

     A 2024 comparative study that still labels O. felineus's Group 3 rating 'noncarcinogenic to humans' and the other two 'Group 1A', a category IARC has never used.

101. 101
     Zaparina OG, Kapushchak YK, Lishai EA, Hong SJ, Sripa B, Pakharukova MY. Species-specific renal and liver responses during infection with food-borne trematodes Opisthorchis felineus, Opisthorchis viverrini, or Clonorchis sinensis.PLoS One · 2024 · 19(12):e0311481doi:10.1371/journal.pone.0311481 · PMID 39637122

     Side-by-side hamster infections in which precancerous bile-duct changes appeared mainly with O. viverrini, a hint that the species differ.