Parasite gives a man cancer

In rare case, a patient’s weakened immune system may have let tapeworm spread disease

PETRIFYING PARASITE Dwarf tapeworms (Hymenolepis nana, shown) can become a horrifying problem for people with weakened immune systems. Cells from one man’s tapeworms turned into cancer cells and spread throughout his body.

Courtesy Peter Olson/Natural History Museum, London

Tapeworms can kick parasitism up a notch to become cancer, a case in Colombia shows.

A 41-year-old man in Medellín went to the doctor complaining of fever, cough, fatigue and weight loss that had lasted several months. Scans revealed tumors in his lungs, liver, adrenal glands, lymph nodes and other spots in his body. The disease looked like cancer, but it puzzled doctors: the small cells in the growths weren’t human cancer cells.

DNA analysis revealed a shock: The cancer cells came from dwarf tapeworms (Hymenolepis nana), pathologist Atis Muehlenbachs of the U.S. Centers for Disease Control and Prevention and colleagues report in the Nov. 5 New England Journal of Medicine. Contagious cancers affect dogs, Tasmanian devils and clams, but this is the first time researchers have found a parasite giving a person cancer.

HIV infection had weakened the man’s immune system so that tapeworm stem cells could grow unchecked, the researchers speculate. Mutations then turned the stem cells into cancer. The case raises concerns that people with weakened immune systems may be in danger of contracting similar tapeworm cancers. “This is a rare disease,” Muehlenbachs says, but “we don’t know how rare.”

Editor’s note: On 11/19/15, this article was updated to correct the spelling of the genus Hymenolepis.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

More Stories from Science News on Health & Medicine