A common tapeworm develops tumors, which can then spread to its human host, according to new CDC research.

The first instance of a parasite spreading its cancer is believed to be rare – but could present health problems in less-developed countries with the unfortunate combination of tapeworm and HIV infections, according to the new study, 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 Atis Muehlenbachs, a pathologist at the CDC’s Infection Diseases Pathology Branch. “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.”

[pullquote]The pathologists are still unsure whether traditional tapeworm drugs or cancer treatments would combat the strange ailment.[/pullquote]

The new observation came from strange biopsies in a patient in Colombia two years ago. Local doctors asked the CDC to investigate the series of bizarre biopsies from the 41-year-old, HIV-positive man.

The tumors in his lungs and lymph nodes looked like human cancer – but found the cells were not human, according to the agency.

The cells were 10 times smaller than normal human cancer – and they were fusing together, something not normally seen in human tumors.

Dozens of tests eventually turned up DNA from the dwarf tapeworm within the tumor. But the man died just 72 hours after the findings.

The pathologists are still unsure whether traditional tapeworm drugs or cancer treatments would combat the strange ailment, they said in a statement.

Dwarf tapeworms, known scientifically as Hymenolepis nana, is found in 75 million people worldwide at any given time, according to the CDC. It’s mostly found in places without sanitation methods or common handwashing practices, the agency added.

The strange transference of the cancer cells is an incredible adaptation, said Peter Olson, a tapeworm expert from the Natural History Museum in London, U.K., who helped identify the genetic material in the Colombian man’s tumor.

“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. “It represents an enormous advance in our knowledge and raises questions about the conditions under which cells may become cancerous.”

The H. nana results who the first parasite cancer spreading to a host. However, certain flatworms apparently increase the chances of developing bile-duct cancer, and other water-borne parasites have been linked to bladder cancers, according to the American society.