Tapeworm Infestation Led to Cancerous Tumors in a Colombian Man's Lungs

Hymenolepis tapeworm
According to the CDC, a man developed tumors made up of cancer cells from a dwarf tapeworm. The tapeworm, shown here, is a common human parasite. Dr Peter Olson/Natural History Museum

A Colombian man developed a cancerous tumor from a tapeworm that grew inside his lungs, scientists at the U.S. Centers for Disease Control and Prevention (CDC) and the Natural History Museum in the U.K. have discovered.

The findings were published in a report titled "Malignant Transformation of Hymenolepis nana in a Human Host" in the November issue of the New England Journal of Medicine. It describes the case of a human who developed cancerous tumors from dwarf tapeworm (Hymenolepis nana) cells.

In January 2013, a 41-year-old man presented himself to a hospital in Medellin, Colombia, with numerous ailments, including fever, fatigue, cough and months' worth of weight loss. He had been diagnosed with HIV infection seven years earlier, and wasn't taking his meds properly. In addition, a stool sample revealed that tapeworm infestation had developed in his body.

Things got much stranger when, after investigating the man's abnormal breathing patterns, the doctors found strange-looking tumors in his lungs—biopsied samples of the tumors showed cells that were much smaller than humans cells. So the Colombian doctors referred the case to the CDC's lab in Atlanta, Georgia.

"It looked like cancer, but the tumors were composed of cells that were not human," Dr. Atis Muehlenbachs, a pathologist at the CDC and the lead author on the report, told NPR. At first, he thought it might have been a slime mold. The CDC, with help from the Natural History Museum in London, spent nearly three years researching the cells. Finally, DNA testing on the tumors confirmed that the tumors were comprised of tapeworm cells.

"We were amazed when we found this new type of disease—tapeworms inside a person essentially getting cancer that spreads to the person, causing tumors," Muehlenbachs said in a statement. He added that while this type of infection is rare, "the potential for this to be a larger, but unrecognized, problem is there. It's definitely an area that deserves more study."

Unfortunately, the patient died within 72 hours of the discovery.

The dwarf tapeworm infects more people than any other tapeworm, with around 75 million people infected at any one time. But in most cases, tapeworm infestations are restricted to the intestine. The researchers have hypothesized that in this particular case, the tapeworms were able to multiply rapidly, and to spread to other parts of the body, due to the man's abnormal immune function.

But it remains unclear how exactly the tapeworm cells started to behave with cancer-like properties. Dr. Peter D. Olson, a tapeworm expert at the Natural History Museum, who collaborated on the research project, has suggested that perhaps the rapid multiplication of the tapeworms allowed enough changes for the mutations to develop over generations. And at some point, instead of dividing in the normal way (to create new, adult tapeworms), the cells became cancerous. "This study is an example of natural history and public health experts working together to uncover fascinating new details about the natural world," Olson said in a statement. "It also raises fundamental questions about the conditions under which cells may become cancerous, whether they're human cells or even those of a parasitic worm."

At the same time, the researchers caution against actually calling this case "cancer." According to The Washington Post, Muehlenbachs refers to it as "an infection with parasite-derived cancer which causes a cancer-like illness."