Transmissible cancer cells are cancerous cells that can spread from one individual to another, typically through direct contact or environmental exposure. This phenomenon has been observed in certain species, such as Tasmanian devils, where a contagious form of facial tumor disease is transmitted through biting. These cells can survive outside the original host and can proliferate in a new host, leading to the development of tumors. Research on transmissible cancer cells helps scientists understand cancer biology and the mechanisms of disease spread, potentially informing treatments for both animals and humans.