Investigation 007
What the Slide Cannot Say
Three parasites cause cancer. Nobody is checking for a fourth.
Flukes & tapeworms
Dwarf tapeworm
In 2015 a man's tumours turned out to be the tapeworm's cancer, not his. One case, and it changed what a tumour can be.
What we are reading
Gathered for the investigation and not yet written up. Each note says what the paper does and does not show.
- Muehlenbachs A, Bhatnagar J, Agudelo CA, Hidron A, Eberhard ML, Mathison BA, Frace MA, Ito A, Metcalfe MG, Rollin DC, Visvesvara GS, Pham CD, Jones TL, Greer PW, Vélez Hoyos A, Olson PD, Diazgranados LR, Zaki SR. Malignant Transformation of Hymenolepis nana in a Human Host.10.1056/NEJMoa1505892 · PMID 26535513
The case that changed what a tumour can be. A Colombian man with HIV had nests of monomorphic undifferentiated cells in lymph node and lung — invasive, crowded, cancer by every morphological criterion — except the cells were far too small to be human. A broad eukaryotic PCR returned HYMENOLEPIS NANA, the dwarf tapeworm. Immunohistochemistry and in-situ probes lit the cells up as tapeworm. Deep sequencing found structural variants in the parasite's genome 'compatible with mutations described in cancer'. So: the tapeworm's cells had become malignant, and the man was carrying a cancer that was not his. Say clearly on air that this is ONE case, in a profoundly immunosuppressed host, and that it does not show parasites cause human cancer. What it shows is narrower and stranger — that a pathologist can look at human tissue, see unambiguous cancer, and be looking at another species.
- Conn DB. Malignant Transformation of Hymenolepis nana in a Human Host [letter].10.1056/NEJMc1600490 · PMID 27028926
The correspondence that followed, from a Harvard comparative-zoology parasitologist. Worth having because it is where the field argued about what the case actually demonstrated, and because it is a reminder that the finding survived expert scrutiny rather than being quietly dropped.
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