Although cancer is not a contagious disease in humans or other vertebrates, there have been rare cases in which cancers have spread from one organism to another. Describe three cases of these contagious cancers and what conditions might have led to their appearance. For an introduction to this topic, see http://www.cancer.org/cancer/cancerbasics/is-cancer-contagious.

Key Concepts

Contagious Cancers

Contagious cancers are rare instances where cancer cells can be transmitted from one individual to another, leading to the development of tumors in the recipient. This phenomenon has been documented in certain species, such as Tasmanian devils and dogs, where cancer cells can spread through direct contact or environmental exposure. Understanding these cases helps illustrate the unique biology of cancer and its potential for transmission under specific conditions.

Environmental Factors

Environmental factors play a crucial role in the emergence of contagious cancers. For instance, close living conditions, social behaviors, and shared habitats can facilitate the transfer of cancer cells between individuals. In the case of Tasmanian devils, aggressive behaviors during mating rituals have been linked to the spread of facial tumor disease, highlighting how ecological and behavioral contexts can influence cancer transmission.

Immune System Evasion

The ability of cancer cells to evade the immune system is a key factor in the development of contagious cancers. Normally, the immune system identifies and destroys foreign cells, but in some cases, cancer cells can develop mechanisms to avoid detection. This evasion allows them to survive and proliferate in a new host, as seen in the transmissible venereal tumor in dogs, where the cancer cells are recognized as 'self' by the recipient's immune system.