Scientists find evidence of new contagious cancer in animals

If there is anything good about cancer, it is perhaps that it's not contagious, not usually anyway. But several recent discoveries have led experts to speculate that eventually some cancers might develop the ability to spread from one person to another.

So far, most contagious cancers are found in nature. One type has so decimated Tasmanian devils that they are in danger of extinction. And now a recent study published in the Proceedings of the National Academy of Sciences (PNAS) shows a second, distinct type of contagious cancer, likely spread by biting or scratching, has also begun to attack the species.

Although those two cancers affect only Tasmanian devils, their existence suggests contagious cancers could be spreading. “More generally, our findings highlight the potential for cancer cells to depart from their hosts and become dangerous, transmissible pathogens. The possibility warrants further investigation of the risk that such diseases could arise in humans,” the researchers wrote.

Scientists have known for many years that wild dogs can contract a contagious form of cancer. And in laboratory studies, mosquitoes have transferred cancer cells from one hamster to another. Last year, scientists reported in the journal Cell they had found a new contagious cancer in softshell clams.

“Our findings suggest that horizontal transmission of cancer cells is more widespread in nature than previously supposed,” the scientists wrote.

Contagious cancer differs from other communicable diseases known to cause tumors such as human papillomavirus (HPV) or hepatitis B. Those diseases cause new instances of cancer to spring up in patients, but communicable cancer originates in one subject and spreads directly to others.

Transmission isn’t always within a species. The New England Journal of Medicine reported three years ago that a man contracted cancer from a tapeworm. The man’s immune system was compromised by HIV.

Thus far, human-to-human transmission of cancer has occurred in only very rare cases or under unusual circumstances.

In 2009, PNAS published a rare case in which doctors diagnosed an 11-month-old girl with a malignant tumor in her cheek. She had contracted the cancer from her mother, who died of leukemia shortly after giving birth. So far only 17 cases of mothers transmitting cancer to their unborn children have been reported; the first was in 1866.

Malignant cells have also transferred from one person to another through organ transplants and surgical contamination. In one case reported in 1996, a surgeon accidentally cut the palm of his hand while he was performing surgery to remove a malignant abdominal tumor from a patient. Five months later, the surgeon developed a malignant tumor on his hand at the site of the injury. Nearly 30 years ago, The New England Journal of Medicine documented the case of a healthy, 19-year-old laboratory worker who developed a malignant tumor in her hand after she accidentally stabbed herself with a syringe full of colon cancer cells.

Those cases obviously occurred in highly unusual circumstances. According to the American Cancer Society there is no evidence that close contact or things like sex, kissing, touching, sharing meals, or breathing the same air can spread cancer from one person to another.