Parasite gives a man cancer

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.