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Can people catch cancer? Not likely, but some animals can

Recent headlines about contagious cancers found in some animals may make you wonder: Could I catch cancer?

Recent headlines about contagious cancers found in some animals may make you wonder: Could I catch cancer? In Australia, Tasmanian devils are dying from aggressive facial tumors caused by a contagious virus. In the Atlantic Ocean, some clams are developing a form of leukemia caused by cancer cells suspended in the water. And scientists have known for years that dogs can spread cancer cells from one to another during intercourse.

"Despite recent headlines about cancer being contagious in other species, current data shows it’s virtually impossible in humans," says Dr. Glen Weiss, Director of Clinical Research and Phase I & II Clinical Trials at our hospital near Phoenix. "There have been attempts to transfect people without cancer with cancer cells, and it did not work."

A controversial experiment

In the 1950s and 1960s, Dr. Chester Southam, a New York immunologist, conducted several controversial experiments by injecting live cancer cells into uninformed cancer patients and healthy prisoners. While patients in both studies grew tumors, those in the healthy patients were quickly attacked and eliminated by their immune systems. "Foreign cells would more likely be rejected just like an organ donation or bone marrow transplant from a donor," Dr. Weiss says. "In order to take, a recipient would likely require significant immunosuppression." Southam was widely criticized for his experiments on humans and his medical license was suspended for one year.

Organ recipients are at a higher risk of developing cancer, but only in rare cases has the cancer been linked to the organ donor having cancer. Such cases are so rare that some cancer patients are still eligible to donate organs. Some recipients develop cancer because the body's immune system is suppressed to help prevent organ rejection. "Fortunately, survival of transplanted cancers in healthy humans is exceedingly rare and documented by only a small handful of cases," Dr. James S. Welsh, a radiation oncologist currently with the Loyola University Health System writes in a 2011 article on contagious cancer. "Thus, friends and family members of cancer patients and we, as caregivers of cancer patients, need not be unduly concerned with the remote possibility of 'catching cancer.'"

Contagious viruses

Humans may spread contagious viruses that lead to cancer. For instance, the human papillomavirus (HPV) is responsible for virtually all cases of cervical cancer. It is also linked to most cases of vaginal and vulvar cancer and more than half the cases of penile cancer. The virus is also linked to 90 percent of anal cancers and 72 percent of oropharyngeal cancer. The hepatitis B and C viruses may lead to hepatocellular carcinoma, the most common type of liver cancer.

Dr. Welsh writes that studying contagious cancers in animals may lead to a better understanding of the disease in humans. Why do dogs with canine transmissible venereal tumor (CTVT) usually fight off the disease, but Tasmanian devils with devil facial tumor disease (DFTD) die within six months? DFTD has wiped out 90 percent of the species. Also, like cancers in humans, DFTD comes in various types, and researchers have found that some Tasmanian devils may develop immunity to some types but not others. "Subtleties of DFTD immunity along with the immunity to CTVT in dogs are important for their pure scientific interest,” Dr. Welsh writes. “Similarly, the natural resistance humans possess against transmitted malignancies … is of scientific interest." Dr. Weiss adds that identifying what may lead to improved immunity to CTVT in dogs or DFTD in Tasmanian devils may hold clues to new or better ways to attack cancers in humans and even other species in veterinary medicine.