Transmissible cancer

A transmissible cancer is a cancer cell or cluster of cancer cells that can be transmitted from animal to animal. They are quite rare in humans. These cancers are distinct from cancers caused by infectious agents such as oncoviruses and cancer bacteria, which are more common.

Cancer is not normally a contagious disease, but there are known exceptions in dogs, Tasmanian devils, Syrian hamsters, and some marine bivalves including soft-shell clams. These cancers have a relatively stable genome as they are transmitted. Because of their transmission, it was initially thought that these diseases were caused by the transfer of oncoviruses, in the manner of cervical cancer caused by HPV.

It has been suggested that animals that have undergone population bottlenecks are at greater risks of contracting transmissible cancers.

Transmissible cancers are rare in humans. A malignant fibrous histiocytoma was contracted from a patient by a surgeon when he injured his hand during an operation. More recently, Barozzi and colleagues found that a significant fraction of Kaposi's sarcoma occurring after transplantation may be due to tumorous outgrowth of donor cells. Although Kaposi's sarcoma is caused by a virus (Kaposi's sarcoma-associated herpesvirus), in these cases, it appears likely that transmission of virus-infected tumor cells—rather than the free virus—caused tumors in the transplant recipients.

Only one instance of cross-species cancer transmission to humans is known, that of a 41-year-old man in Colombia with a compromised immune system due to HIV. The man's tumor cells were shown to have originated from the dwarf tapeworm, Hymenolepis nana, making this a case of parasite-to-host cancer transmission.

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