Cancer is not contagious in humans but another form of cancer that is transmissible in animals has been found. While a healthy human cannot “catch” cancer from someone who has it without a transplant of an organ or tissue with cancer cells, the fact that contagious forms of the disease are being discovered highlights how little is still known about cancer and whether it could eventually be infectious in humans.
Scientists researching cancer have found evidence that cancer cells are being passed between three very different animal species – Tasmanian devils, soft-shell clams and dogs –through physical contact, such as biting or sex. The living cancer cells are jumping from one animal to another like a parasite or virus would spread.
Researchers had identified a contagious cancer in 1996 that was decimating the population of Tasmanian devils. Now, they have found a second type of infectious cancer in the endangered, small dog-sized marsupials, which they announced in the latest Proceedings of the National Academy of Sciences journal. The new cancer has chromosomal changes that are clearly different from the first disease.
Further stumping researchers is the fact that the contagious cancers in dogs and Tasmanian devils evolved independently and are different. The two types of contagious cancers in the marsupials have some similarities. The Devil Facial Tumor Disease (DFTD 1 and 2) recently emerged and aggressively causes tumors on the face and neck that kills the animal within months. Due to their small population and geographic isolation, the devils are genetically similar, which probably allows the tumor cells to prosper. Conversely, Canine Transmissible Venereal Tumor (CTVT) is a sexually transmitted disease that is seen worldwide and has been around for a long time.
DFTD has quickly spread through devil populations on the island of Tasmania, which is an Australian state. However, when one devil displayed tumors that were not typical of DFTD, they discovered the second cancer, which has now been seen in at least 8 of the mammals.
In an attempt to save the species, experts are trying to breed devils they have identified as immune to the first cancer they found and keep them separate from the rest of the population. They are also working on a vaccine, but those plans now need to incorporate the newly identified contagious cancer to protect and save the animals.
The discovery of cancers that can be transmitted raises questions as to where this has always been true or cancer cells have evolved or mutated much like viruses do. Could forms eventually jump species like viruses have (e.g., swine flu, Ebola)?
In humans and most species, cancer occurs when abnormal cells begins to divide and spread uncontrollably destroying healthy cells in its wake. It can spread to other parts of the body, i.e. metastasize. Also, in humans, there are viruses that are contagious that often lead to cancer, but it is the virus that is passed on, such as certain human papilloma viruses (HPVs) and the human immunodeficiency virus (HIV).
As Gregory Woods, a University of Tasmania immunologist who co-authored the study, noted, “Transmissible cancers are extremely rare, but for two [to occur] in the one species, astonishing.” The contagious cancers that are not virus-related in the other species has experts stumped and the finding of another form has them questioning whether transmissible cancers are more common than previously thought.
Written and edited by Dyanne Weiss
American Cancer Society: Is Cancer Contagious?
Nature: Oncogene: Clonally transmissible cancers in dogs and Tasmanian devils
UPI: Second form of contagious cancer found in Tasmanian devils
NPR: Startling New Evidence Cancer Is Contagious
Photo of Tasmanian devil by Willis Lim – courtesy of his Flickr page – Creative Commons license