In a case that doctors are describing as “crazy,” a 41-year-old Colombian man was found to host cancerous tapeworm tumors in his brain and other bodily organs.

The man, who recently died of complications arising from HIV, was first diagnosed back in 2013. Doctors struggled to make sense of the tumors disbursed throughout his body, the cells of which were uncharacteristically small, densely packed — and apparently not human.

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Further analysis by the U.S. Centers for Disease control confirmed that the patient had contracted the cancerous cells from the tapeworm, Hymenolepis nana, and that owing to his compromised immune system, the tumors were allowed to flourish. The details of this extraordinary case can now be found in the latest edition of The New England Journal of Medicine.

Short video produced by the CDC explaining the case.

The CDC suspects that the patient contracted the cancer by ingesting some microscopic tapeworm eggs, likely in food contaminated by mouse droppings, insects, or human feces. It’s not known if the cells in the tapeworm eggs were already cancerous before they entered the patient’s body, or whether there was some kind of biological interaction between the parasite and the body that converted them into cancerous cells.

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Prior to this discovery, scientists didn’t think that any human parasite could harbor cancer cells, or transfer them to people. What’s more, cancer is not generally considered to be a transmissible disease, though precedents exist in the animal kingdom, including transmissible cancer cells in Tasmanian Devils and domestic dogs.

Cancerous parasitic worm cells (Credit: A. Muehlenbachs et al., 2015/NEJM)

“This is the first time we’ve seen parasite-derived cancer cells spreading within an individual,” noted expert pathologist and study lead author Atis Muehlenbachs in the Washington Post. “This is a very unusual, very unique illness.” Muehlenbachs specializes in unexplained mystery illnesses and deaths.

The cancer had spread to other organs of the patient’s body (Credit: A. Muehlenbachs et al., 2015/NEJM)

As reported in the Washington Post, this discovery has some scientists worried, though the CDC doesn’t believe there’s any risk of the tapeworm cancer cells being spread among humans. This may represent a unique case in which a particularly vulnerable individual was left susceptible. More from WaPo:

It’s unclear how common this type of tapeworm cancer illness is in humans, but experts like Pritt believe it’s likely that there are more cases out there: “H. nana is a very common tapeworm infection in humans, and therefore I would expect there to be other cases like the one described…that were misdiagnosed or went undetected.”

Matthew B. Laurens, an associate professor at the University of Maryland School of Medicine who specializes in infectious diseases, said the findings highlight our need to strengthen cancer diagnosis and data collection in developing countries.

“We could just be scratching the surface of something that could be very important,” Laurens said.

Peter D. Olson, a researcher at the Natural History Museum in London who helped the CDC interpret its results, said that the finding represents “an enormous advance in our knowledge and raises questions about the conditions under which cells may become cancerous.”

Some medical experts caution that the term “cancer” isn’t even appropriate in this context. Muehlenbachs himself prefers to describe it as “an infection with parasite-derived cancer which causes a cancer-like illness,” while asking: “Can you say a worm has cancer? That’s a philosophical question, how you define this.”

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Much more at the Washington Post. Read the entire study at The New England Journal of Medicine: “Malignant Transformation of Hymenolepis nana in a Human Host”.


Email the author at george@gizmodo.com and follow him at @dvorsky. Top image by A. Muehlenbachs et al., 2015/NEJM)