2. Tasmanian devils and dogs can catch cancer too
Researchers have discovered eight different transmissible cancers so far². Two in Tasmanian devils, one in dogs, and the rest in bivalve molluscs.
The Tasmanian devil cancers are facial tumours, passed between the devils when they bite each other, which they do frequently. Like the clam cancer, it hasn’t evolved from the mutated cells of the individuals it lives in. It’s deadly, and has pushed the creatures towards extinction, though scientists have recently discovered that the devil’s immune system is fighting back, and their numbers are stabilising.
A form of contagious cancer also affects stray dog populations - canine transmissible venereal tumours (CTVT). This cancer is thought to have arisen from an individual dog 11,000 years ago, termed the ‘founder dog’. The tumours are sexually transmitted, and are seen in stray dog populations in all corners of the world, though curiously not in dogs living in the exclusion zone around the Chernobyl nuclear power plant.
These transmissible cancers have been likened to parasites, life-forms in their own right, spreading from host to host.
Cancer has never been passed from animals to people, but there have been extremely rare cases of person-to-person transmission of cancer. It has only been reported a handful of times - during an organ transplantation, experimental treatment and a surgical accident.
It remains a mystery how transmissible cancers form and exist at all.