Tapeworm spread cancer cells to man

Scientists have reported the first case of a human falling ill from cancer cells that arose in a parasitic tapeworm.

U.S. researchers say cancer cells originating in a common tapeworm took root in a 41-year-old Colombian man who was HIV positive.

A brief report on the case is published in Wednesday's issue of the New England Journal of Medicine. The researchers describe tapeworms growing in a person and essentially spreading cancer.

In 2013, doctors in Colombia asked the CDC for help to diagnose the cause of the man's lung tumours. He had sought medical care because of fatigue, fever, cough and several months of weight loss. He was not taking treatment for HIV.

Unlike human cancer cells

CT scans showed growths in the lungs, liver and adrenal glands. The tumours resembled human cancer, but the CDC scientists found they were not.

"They were way too small to be human," said the study's lead author, Dr. Atis Muehlenbachs, a pathologist at the U.S. Centers for Disease Control and Prevention in Atlanta. "They were actually about 10 times smaller than a human cancer cell."

The tumour cells also seemed to be fusing together, which human cancer cells normally don't do. 

It took a lot of laboratory sleuthing to discover the real cause.

They eventually found DNA from H. nana tapeworms in the man's tumour that invaded tissues.

During the lab investigations, the man's lymph nodes increased to a maximum of five centimetres in diameter and his condition deteriorated over four months until he died. Before the patient died, he gave written permission for studies to be performed and the results to be published.

This tapeworm species completes its whole life cycle in an individual's small intestine. In people with weakened immune systems, large numbers of tapeworms can develop in the intestine because they aren't able to fight off the parasite effectively.

The researchers suspect the mechanism used by the parasite to avoid our immune system also allowed the tapeworm's cells to proliferate unchecked in the Colombian patient, ultimately leading to the tumour.

Muehlenbachs said while this type of event is rare, the tapeworm is found worldwide and there may be more cases that are unrecognized in people globally who have conditions that weaken their immune system. 

The uniqueness of the case lies in how the tumour cells seem to have been transmitted by the tapeworm itself. But other infectious agents such as the human papillomavirus (HPV) and H. pylori also contribute to cancer in humans. 

 Dr. Len Lichtenfeld, deputy chief medical officer for the American Cancer Society in Atlanta, said the new findings raise the possibility of using the same tools to try to understand the relationship between various infections and cancer.

More immediately, Muehlenbachs, said the case is a reminder of the importance of handwashing and drinking safe water when travelling to avoid dwarf tapeworm infections.