Ancestral cell infects dogs with contagious tumours

A tumour that can spread between dogs has been identified by scientists who believe it may have implications for the transmission of human cancers.

The scientists found that a type of canine cancer, known as Sticker's sarcoma, originated in a single dog several centuries ago and has been passed on during sex or close contact.

Although some human cancers are triggered by infectious viruses, this unusual canine tumour appears to have been propagated by transmission of individual tumour cells. When a canine tumour cell enters an unaffected animal it begins to divide uncontrollably and develop into a tumour.

The study, in the journal Cell, examined tumour cells from 16 unrelated dogs in Italy, India, Kenya, Brazil, the US, Turkey and Spain. The scientists found the DNA from the tumour cells did not match the DNA from the dogs, which should have been the case.

The scientists believe the cells came from a dog that had lived between 250 and 1,000 years ago and may have been transmitted through sexual contact or by areas affected by the cancer being licked, bitten or sniffed.

Professor Robin Weiss, of University College London, said the tumour is not normally fatal and usually regresses within three to nine months, leaving the dogs immune to reinfections.

"On rare occasions, cancer cells have been transmitted from one human to another in organ transplants," he said. "Because the recipient is treated with immunosuppressants to prevent rejection, the transferred cancer cells can grow into tumours just like canine tumour."