Journal club: Patient diagnosed with non-human cancer

In a fascinating case report in the New England Journal of Medicine, Muehlenbachs et al identified a patient with disseminated cancer through the lungs and lymph nodes. The major oddity of the cancer was the small size of the cells, far smaller than human cells, indicating that the cancer cells were non-human. Extensive analysis identified the cancer cells as coming from Hymenolepis nana, the dwarf tapeworm. The patient was infected with tapeworms, one of which developed cancer (as can happen to any organism). These tapeworm cancer cells then metasized from the tapeworm into the host, adapted to the host and spread throughout the body as a foreign cancer. While the immune system is normally highly effective at clearing foreign organisms from the body, the tapeworm cancer cells were able to survive and disseminate throughout the body, possible for a combination of three reasons: i) tapeworms induce immune tolerance against their antigens, ii) the tumour cells were selected to be of low immunogenicity, and iii) the patient was HIV+ and immunodeficient. While this may be a one-off case, since parasite infections are so common perhaps we will find non-human cancers in other patients?

Muehlenbachs et al. 'Malignant Transformation of Hymenolepis nana in a Human Host'. New England Journal of Medicine. 2015. 373:1845