Generally, cancers cannot be transmitted from one person to another. However, among certain animal species, a few rare types of cancer can be passed, such as bacterial or viral infections.
Can Cancer Become Contagious?
According to the American Cancer Society, a person cannot catch cancer from someone else. It cannot be spread through close contact or practices such as touching, kissing, sex, sharing meals, or breathing the same air.
Typically, cancer is a threat that comes from within. Cell mutations can cause them to multiply out of control while preventing the natural defense mechanism of the body. When this happens, a mass called a tumor develops, which can be fatal if not treated.
Tumors from a person with cancer do not have the ability to live in the body of another healthy person. This is because an individual's immune system can locate and destroy foreign cells, including those from another person.
When Cancer Spreads Through Touch
While tumors do not spread beyond their human host, that is always the case in animals. There are a few animal cancers which are easily transmissible which can even pose an existential threat to its host species.
For instance, transmissible animal cancers spread among Tasmanian devils in Australia. Known as Devil Facial Tumor Disease (DFTD), this type of cancer spreads through skin contact and is usually transmitted between males during violent fights over mates. In DFTD, the cancerous lesions quickly grow and kill the animals as soon as they grow large enough to restrict eating or breathing.
It is thought that Tasmanian devils spread cancer cells because they lack genetic diversity. This makes it harder for their immune systems to identify cells from different animals apart. As a result, the cancer cells survive and multiply in number undetected.
As of 2014, Devil Facial Tumor Disease had reduced the population of Tasmanian Devil by 80%, posing a threat of possible extinction. Still, there is hope for these animals in the form of immunotherapy treatments. A recent study also suggests that DFTD may not completely wipe out Tasmanian devils but may only make them evolve to better survive the disease.
Another type of transmissible cancer can be found in dogs. Known as canine transmissible venereal tumor (CTVT), this cancer usually forms on or near the dog's genitals and spreads during mating. CTVT is not deadly, and the tumor typically regresses and disappears on its own.
Experts believe that canine transmissible venereal tumor first appeared from 8,000 to 11,000 years ago, with the same cell lineage still living in modern dogs. This could be due to the fact that this disease has the unique ability to infect canines without causing much harm to them. Since the tumor cells do not kill their hosts, they have a better chance to get passed on.
A few other animal species are known to carry transmissible cancer, but scientific study on them is limited. A 1964 study reports that there is a type of transmissible cancer in Syrian hamsters and various species of bivalves.
More cases of transmissible cancer await discovery. For now, scientists focus on fighting the cancers that develop within humans and not those that come from outside sources.
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