HealthDay News — Cancer cells transmitted from a common tapeworm appear to have caused cancer-like tumors in a Colombian man with HIV — the first known case of malignant transformation, U.S. health officials report in the New England Journal of Medicine.

The parasite — known as Hymenolepis nana, or the dwarf tapeworm — is the most common human tapeworm worldwide, particularly in developing nations. At any given time, up to 75 million people carry it, according to the U.S. Centers for Disease Control and Prevention. People can become infected with dwarf tapeworm eggs when they eat food contaminated with mouse droppings or insects, or ingest fecal matter from people carrying the parasite.

Most cases are asymptomatic; however, in some cases, the dwarf tapeworm can continue to reproduce itself in the intestines, according to the report.

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In the case of the man with HIV, CDC scientists suspect that his weakened immune system allowed the dwarf tapeworm to thrive unchecked. From there, mutations may have accumulated in some tapeworm cells — essentially causing cancer in the parasite — and those cells eventually caused cancer-like tumors in their human host.

That, at least, is the theory, according to Atis Muehlenbachs, MD, PhD, one of the CDC researchers.”There’s still a lot we’d like to learn,” Muehlenbachs told HealthDay.


1. Muehlenbachs A, Bhatnagar J, Agudelo CA, et al. Malignant Transformation of Hymenolepis nana in a Human Host. N Engl J Med. 2015; 373:1845-1852.


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