Recent scientific research reveals that certain types of cancerous tumors possess the rare ability to spread between living organisms like infectious diseases, bypassing the immune barriers that typically reject foreign cells. Documented across species including dogs, Tasmanian devils, clams, and fish, these transmissible cancers challenge traditional understandings of how tumors develop, evolve, and evade detection by host immune systems.
Transmissible Tumors in Dogs and Tasmanian Devils
Unlike standard cancers that originate and develop entirely within a single patient’s body, transmissible cancers rely on living cells that pass between hosts and continue to reproduce. According to research reported by Knowable Magazine, these infectious cell lines must overcome the host immune system’s natural tendency to destroy unfamiliar tissue.
In response to this challenge, certain transmissible tumors have evolved mechanisms to disable immune-related genes or mask the proteins that signal abnormal cells. For instance, canine transmissible venereal tumor (CTVT)—first described during the 19th century and primarily spread through direct contact during mating—reduces the surface expression of major histocompatibility complex class I (MHC-I) proteins to evade immune surveillance. Similarly, devil facial tumor disease spreads among Tasmanian devils through biting during aggressive interactions, posing a threat to the carnivorous marsupial populations in Australia and prompting intensive research.
Marine Cancers in Clams and Fish
The phenomenon extends beyond mammals into aquatic environments. In 2015, researcher Michael Metzger identified a transmissible cancer affecting bivalve mollusks, causing a leukemia-like condition in certain types of clams. Joëlle Brown, a researcher specializing in evolutionary ecology at the Moffitt Cancer Center in Florida, notes that tumors arise when cells abandon their natural functions and multiply uncontrollably.
Parallel findings emerged from studies of catfish in Lake Memphremagog on the United States-Canada border, where researchers identified genetically uniform black skin tumors. Researchers emphasize a clear scientific distinction between transmissible cancer cells and viral or environmental carcinogens, confirming that these animal cases do not indicate that human cancers are generally contagious through routine daily contact.
Frequently Asked Questions About Transmissible Cancers
How do transmissible cancer cells survive inside a new host?
Transmissible cancer cells evade the new host’s immune system by suppressing immune-response genes or reducing the display of surface proteins like MHC-I, which normally allow the body to flag and destroy foreign cells.
Can humans contract cancer from animals or other people?
No evidence indicates that human cancers are contagious or capable of spreading between individuals through everyday contact, as transmissible cancers remain exceedingly rare and specific to particular animal species.
What is the oldest known transmissible cancer?
Canine transmissible venereal tumor (CTVT) is one of the oldest known examples of this phenomenon, having been described during the 19th century.