First known transmission of cancer cells from parasite to human identified: U.S. CDC

Scientists at the U.S. Centers for Disease Control and Prevention (CDC) said Wednesday they have found the first known case of a person becoming ill from cancer cells that arose in a common parasite.

The study, published in the New England Journal of Medicine, showed that cancer cells originating in a tapeworm called Hymenolepis nana took root in a 41-year-old man who was HIV positive, causing cancer-like tumors.

The results raised concern that other similar cases, if they occur, may be misdiagnosed as human cancer, especially in less developed countries where this tapeworm is widespread.

"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," lead author Atis Muehlenbachs of CDC's Infectious Diseases Pathology Branch said in a statement.

"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."

The case was first reported in January 2013, when doctors in Colombia asked the U.S. CDC to help diagnose bizarre biopsies from the patient's lung tumors and lymph nodes.

The tumors looked similar to a human cancer, but initial CDC lab studies revealed the cancer-like cells were not human.

The growth pattern was decidedly cancer like, with too many cells crowded into small spaces and quickly multiplying, the U.S. CDC said. But the cells were tiny -- about 10 times smaller than a normal human cancer cell.

The researchers also noticed cells fusing together, which is rare for human cells.

As a result, researchers initially questioned whether it was an unusual cancer or an unknown infection.

After dozens of tests, they eventually found DNA from Hymenolepis nana tapeworms in the man's tumor in mid-2013. Unfortunately, the man died 72 hours later.

The researchers cautioned that drugs to treat tapeworm infections may not be effective against tapeworm cancer cells in people, but human cancer treatments may be beneficial.

Hymenolepis nana infects up to 75 million people at any given time, making it the most common tapeworm infection in humans.

People get the tapeworm by eating food contaminated with mouse droppings or insects or by ingesting feces from someone else who is infected.

Most people show no symptoms, but in people whose immune systems are weak, including people who have HIV or are taking steroids, the tapeworm thrives. Enditem