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An Anonymous Coward writes:

In January 2013, a 41-year-old man in Medellín, Colombia, presented with fatigue, fever, cough, and weight loss of several months’ duration. He had received a diagnosis of HIV infection in 2006 and was nonadherent to therapy ... Stool examination revealed H. nana eggs and Blastocystis hominis cysts. Computed tomographic imaging showed lung nodules ranging in size from 0.4 to 4.4 cm, as well as liver and adrenal nodules and cervical, mediastinal, and abdominal lymphadenopathy.

This case posed a diagnostic conundrum. The proliferative cells had overt features of a malignant process — they invaded adjacent tissue, had a crowded and disordered growth pattern, and were monomorphic, with morphologic features that are characteristic of stem cells (a high nucleus-to-cytoplasm ratio) — but the small cell size ([less than] 10 μm in diameter) suggested infection with an unfamiliar, possibly unicellular, eukaryotic organism.

Although the cells were unrecognizable as tapeworm tissue, immunohistochemical staining and probe hybridization labeled the cells in situ. Comparative deep sequencing identified H. nana structural genomic variants that are compatible with mutations described in cancer. Invasion of human tissue by abnormal, proliferating, genetically altered tapeworm cells is a novel disease mechanism that links infection and cancer.

A severely immunosuppressed man, due to an HIV infection, died as a result of an atypical Hymenolepis nana infection. It appears that the some of the tapeworm cells became cancerous and spread to the patient where they formed tumors. This is the first reported case of cancer in multicellular parasites in addition to the first reported case of transmission of such a cancer to a human.

http://www.nejm.org/doi/full/10.1056/NEJMoa1505892 [nejm.org]

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