A strange form of cancer is being transmitted as an infectious agent among the world’s dogs, without help from viruses or bacteria, a research team in England has found.
The discovery, reported in the journal Cell, shows how a single cancer cell can become a successful parasite, grow and then spread worldwide in susceptible animals. The researchers said the disease is apparently transmitted sexually. It arose in wolves as much as 2,500 years ago, then spread to coyotes and dogs.
The new study is the first to document cancer being spread from animal to animal on its own. Viruses are known to cause some cancers when they damage critical genes during infection. But now it’s clear cancer can get around solo, then spread through a population.
Stephen O’Brien, chief of the Laboratory of Genomic Diversity at the National Cancer Institute, called the discovery “a rich opportunity” to learn more about cancer and infectious diseases. Weiss and his colleagues in London added that the dog tumors also may be spread via licking wounds, sniffing or dogs biting each other.
Fortunately, even though the tumors grow aggressively at first, they eventually shrink and then succumb to the host dog’s immune system. Remarkably, after the cancer has disappeared, the dogs have gained protective immunity, which blocks further infection by the cancer cells. The dogs’ blood also can be used to vaccinate other dogs and block infection.
Genetic tests done on the tumor cells showed all the cases – called Sticker’s sarcoma – originated from a single mutant cancer cell, and in hundreds of years it has grown and spread everywhere in dogs. It also means it’s now the oldest cancer known to science.
According to Bridgett vonHoldt, at the University of California at Los Angeles, and Elaine Ostrander at the National Institutes of Health, in Maryland, “the prospect of a contagious cancer cell is at once intriguing and frightening.” But in any case, the two wrote in Cell, “if and when a more toxic contagious cancer emerges, we should not be surprised. Ever vigilant, man’s best friend has warned him of dangers to come.”
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