Tapeworms and Cancer: A Health Horror Story

Tapeworms might have passed cancer cells to patient


To those of you with a phobia of parasites of the wriggling variety: You were right — they're terrifying.

Here's why: Centers for Disease Control and Prevention (CDC) researchers think a tapeworm might have passed its own cancer cells into a human host. This case study was published Nov. 5 in The New England Journal of Medicine.

“We were amazed when we found this new type of disease — tapeworms growing inside a person essentially getting cancer that spreads to the person, causing tumors,” said lead study author Atis Muehlenbachs, MD, PhD, staff pathologist with the CDC’s Infectious Diseases Pathology Branch, in a press release. “We think this type of event is rare. However, this tapeworm is found worldwide and millions of people globally suffer from conditions like HIV that weaken their immune system. So there may be more cases that are unrecognized. It’s definitely an area that deserves more study.”

OK, so it's probably rare — it's the "first known case of a person becoming ill from cancer cells that arose in a parasite," according to the CDC. Still, it's "unsettling," as The Washington Post described it.

'It was hard to convince ourselves that it was true," Dr. Muehlenbachs told dailyRx News. "A prior case with some similar findings was reported from a man in San Francisco in 1996, so we were confident in reporting the initial results ..."

For those with strong stomachs, here's what happened in the current case: A Colombian man, 41, got really sick a few years ago. He already knew he was HIV-positive, and he wasn't sticking to his medications for the disease. But doctors in Colombia took a closer look and found that the man had cancer tumors in his body — but they didn't look quite like normal tumors. The cells were 10 times smaller than human cancer cells, according to the CDC.

So the Colombian doctors reached out to the CDC for help. This is when things turned bizarre: CDC tests revealed that the cancer cells weren't human.

Researchers then began a several-month journey to find out what was wrong. What they eventually found was that the man's tumors contained DNA from dwarf tapeworms.

Seventy-two hours after the researchers discovered the tapeworm DNA, the man died.

This case was unexpected, Dr. Muehlenbachs said.

"To our knowledge, cancer cells directly from a parasitic organism making someone sick had not been theorized before in the medical literature," he said.

As many as 75 million people around the world are infected with dwarf tapeworms at any given time, according to the CDC. The infection often comes from food that's contaminated with mouse droppings or infected insects. In patients with compromised immune systems — like the Colombian patient with HIV — the dwarf tapeworm can thrive. And it's the only type of tapeworm that can live its entire life in your small intestine.

Dr. Muehlenbachs and team theorized that the patient's HIV — and resulting weakened immune system — might have contributed to this bizarre case. And although this case is strange and likely rare, researchers are already trying to come up with ways to fight similar cases in the future. Dr. Muehlenbachs noted that past studies on tapeworm genetics showed similar drug targets for cancer treatment.

The authors of this case study disclosed no funding sources or conflicts of interest.