KELLY MCEVERS, HOST:
A strange medical case was published today in the New England Journal of Medicine. As NPR's Rae Ellen Bichell reports, it challenges our understanding of cancer.
RAE ELLEN BICHELL, BYLINE: In January 2013, a 41-year-old man came to a hospital in Medellin, Colombia. He was in bad shape. He had HIV but had stopped taking his medications a few months before. He'd lost weight, had a fever, he also had trouble breathing. And when doctors tried to find out why, they came across what looked like tumors on his lungs, but the samples looked really weird.
ATIS MUEHLENBACHS: It looked like cancer but composed of cells that were not human.
BICHELL: That's Atis Muehlenbachs, a pathologist at the Centers for Disease Control and Prevention. He's the lead author on the report. Doctors in Colombia had sent Muehlenbachs samples from the patient's lesions. At first, he thought it was a slime mold.
MUEHLENBACHS: Single sheets and clumps of cells and cells growing individually within tissues just completely - like, we thought they were a single-celled organism.
BICHELL: Eventually, DNA tests confirmed the tumors were made of tapeworm cells. They had formed blobs on his lungs, liver and adrenal glands. Lymph nodes had swollen in the patient's neck to the size of golf balls, making it hard for him to move his head. Muehlenbachs said he knew that parasites could have tumors...
MUEHLENBACHS: But the fact that one can invade and disseminate in a human and make them sick really defied belief.
BICHELL: Peter Olson is a biologist at the Natural History Museum in London who took part in the research. He says the dwarf tapeworm lives in the guts of some 75 million people.
PETER OLSON: But it doesn't typically cause problems.
BICHELL: An otherwise healthy person with the tapeworm might not have any symptoms at all. But Olson studied a couple rare cases where like this one, things went south.
OLSON: One of them also involved an HIV patient. It was a man in California. There was another one where the patient was on immunosuppressing drugs because he was receiving a transplant.
BICHELL: Both died. In each case, the patients suffered from a double whammy - a tapeworm infestation and a downed immune system. In this case, Olson says, larval cells normally meant to divide rapidly to create a new tapeworm, went awry.
OLSON: They never actually develop into a worm but instead, they just proliferate as a cancer.
BICHELL: And the patient's weak immune system couldn't contain the cells inside the gut as it usually did. Muehlenbachs says that clinicians all over the world should be aware of this possibility.
MUEHLENBACHS: We don't know how rare this disease is. It's the most common tapeworm worldwide, and HIV is also very common. So we're very eager to learn about other cases and potentially those that we might have an opportunity to attempt treatment.
BICHELL: That's the particularly sad thing about this case. They never had a chance to treat the patient. For months, he had asked what was going on in his body. But days before the CDC figured out that it was tapeworm cancer, the man slipped into a coma. Within 72 hours after the diagnosis came in, he died.
MUEHLENBACHS: It was heartbreaking.
BICHELL: Muehlenbachs says it's unclear what treatment would help in these situations. Chemotherapy, like for human cancer, or antibiotics to fight tapeworm infections. Rae Ellen Bichell, NPR News.
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