Transmissible tumors are unusual cancers that can spread between individuals, typically through direct contact or environmental exposure. These tumors are most commonly observed in certain species, such as dogs and clams. The cancer cells can survive outside the original host and infect new individuals, leading to the development of tumors in the recipient. One well-known example is Canine Transmissible Venereal Tumor (CTVT), which affects dogs and is transmitted through sexual contact. Another example is Devil Facial Tumor Disease (DFTD), which affects the Tasmanian devil and is spread through biting. These tumors challenge traditional views of cancer, highlighting the complex interactions between cancer cells and their hosts.