Transmissible cancer refers to a rare phenomenon where cancer cells can be transferred from one individual to another, leading to the development of cancer in the recipient. This occurs in certain species, such as Tasmanian devils, where a contagious form of facial tumor disease spreads through biting. Another example is Canine Transmissible Venereal Tumor (CTVT), which affects dogs and is transmitted through sexual contact. In these cases, the cancer cells can survive outside the original host and continue to grow in a new host, highlighting a unique aspect of cancer biology that challenges traditional understanding of the disease.