CDC study: Tapeworms could spread cancer cells to human hosts

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The CDC found that tapeworms could transmit cancer cells to human hosts

(Nov. 5, 2015) – Scientists at the Centers for Disease Control and Prevention solved a puzzling case leading to the discovery that tapeworms could spread cancer cells to their human hosts.

In 2013, doctors in Colombia were stumped after a 41-year-old man with HIV and a weakened immune system had tumors that looked similar to human cancer but appeared to originate from another source. The man had complained of a stomach ailment.

For almost three years, researchers tried to crack the case. What they found will likely make you squirm just a bit. In effect, they discovered that cancer cells from a common tapeworm could take root in people with weakened immune systems, resulting in cancer-like tumors.

“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 Atis Muehlenbachs, M.D., Ph.D., staff pathologist in CDC’s Infectious Diseases Pathology Branch (IDPB). “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.”

Muehlenbachs helped author a report about the case that appears in the Nov. 5 issue of the New England Journal of Medicine. The particular parasite in question for the case was Hymenolepis nana, the dwarf tapeworm that’s the most common in humans.

Researchers wondered if what they were seeing was an unknown infection. But they continued to work the case and discovered too many cancer cells were crowded into small spaces and quickly multiplying. The cell were also about 10 times smaller than a normal human cancer cell and were fusing together, which is rare for human cancer cells.

After dozens of tests, they found DNA from the tapeworm in the man’s tumor. The man died three days after they made the discovery.

Doctors acknowledge that treating a similar ailment could pose challenges. Drugs taken to treat tapeworm infections may not be effective against tapeworm cancer cells in people. It’s possible that human cancer treatments could be beneficial, although doctors said more study was needed.

The type of tapeworm at the center of the case infects up to 75 million people at any given time. People contract them by eating contaminated food or ingesting feces from someone who’s infected. Most people don’t show symptoms; however, tapeworms thrive in people with weak immune systems.

H. nana infections are most common in situations where sanitation and handwashing are problematic, such as developing countries.