One of the first things a medical student learns about cancer is that it not a contagious disease. That this view doesn’t always hold true was proven by a study by Claudio Murgia, Robert Weiss and colleagues in 2006.
Cancers start with gene mutations in a cell of the body. The genes usually affected are important for the control of cell division – when they are damaged the cell escapes the control of the body and starts dividing aggressively, finally forming tumors that can invade and damage the organs and the whole organism. The reasons for the mutations are manifold: radiation, chemicals and microorganisms are among the culpable. And while these, like the virus causing Cervical cancer and the bacterium causing Stomach cancer, can be passed from person the person, it is not cancer itself, but its cause that is being transferred. The study of Mr Murgia showed for the first time that a type of cancer, Canine transmissible venereal tumor (CTVT) is exclusively passed by physical transfer of the cancer cells themselves.
For proving this, the London based scientists took DNA from cancer and normal cells of 40 dogs from 5 continents. When comparing the DNA samples, the researchers found that cancer cells are genetically different from their hosts and quite similar to each other. The researchers concluded that the different cancers are all progeny of a single cell that appeared more than 200 years ago. The cancer cells are being passed during sex.
The study was the first to convincingly describe a contagious cancer. This January, another example of infectious cancer affecting Tasmanian devils was described by Elizabeth Murchison, Anthony Papenfuss and colleagues.
The cancer is transmitted by biting and is highly aggressive, leading to death within months, threatening to extinguish Tasmanian devils in the wild within 50 years. The scientists hope that their results can lead to the development of a vaccine against the cancer cells.