The Catching Kind of Cancer

In 1996 a surgeon was operating on a rare malignant tumor when he accidentally cut himself.  Some months later he developed an identical tumor at the very spot he had injured. Fortunately, this new cancer responded to treatment. Still, the idea of this means of cancer genesis--a "catching cancer" if you will--was mind boggling at the time.  Mind you, this was the height of the HIV era and we were seeing a lot of patients with Kaposi's sarcoma (another cancer) and we were performing biopsies and bronchoscopies on patients with these malignancies, so the idea of  a "catching cancer" was alarming. Could tumors accidentally be aerosolized and inhaled in the course of such a procedure?

Of course, the notion of cancers spreading from one person to another is not new, but it always involves a virus. An example would be papilloma virus which causes venereal warts and which can predispose to cervical cancer. Kaposi's sarcoma (which is now rare for me to see in North America) proved to be related to sexual transmission of HHV-8, a human herpes virus.  But for a cancer to spread from one person to another in the absence of a virus would be remarkable, which is why the report of the surgeon getting inoculated with a cancer through a skin cut was memorable.

There is, however, one animal species at least where such "catching cancer" occurs commonly. Tasmanian devils are prone to something called Tasmanian Devil Facial Tumor. Tasmanian devils, in keeping with their cartoon reputation and their colorful name, are ornery, combative creatures, prone to biting each other. But it's not the internecine warfare that's threatening the existence of the species, but instead a peculiar cancer of the face and jaws, a cancer that seems to sprout from the very spot where one devil was bitten by another.

Careful research by Elizabeth Murchinson and a group of scientists, reporting in the journal Science, suggests that Tasmanian Devil Facial Tumor is truly unique in that it is not a virus causing the transmission. Instead, the work of these scientists suggests that one day, perhaps two decades ago, a cell became cancerous in one Tasmanian devil. The cancer grew and probably killed the original animal but not before that devil had bitten another devil and allowed the cancer to graft on to the new host.

In that sense, the Devil Facial Tumor is truly like a transplant of an organ. But most transplants of organs are rejected  by the immune system unless the host is a twin; it is possible that Tasmanian devils are pretty inbred and therefore genetically very much alike so that the cancer cells are not rejected the way a transplant from an unrelated donor would be rejected.

The only comparable "catching cancer" is one in dogs that is sexually transmitted; this is an ancient cancer and it does not always result in death; it can even regress. Sadly for the Tasmanian devils, the Devil Facial Tumor might be cause for the eventual extinction of the species. The population is already down by 70%.

I found the Tasmanian Devil Facial Tumor story to be a fascinating piece of research, a good explanation of a novel means of cancer development.  Often, in isolated case reports--such as that of the surgeon who nicked himself and developed the very tumor he had cut out from a patient-- we get an insight into a previously unknown mechanism of disease.
As for the Tasmanian devils, it's a shame they are so alike genetically.  That might explain why they fight a lot--no peaceful tribe has emerged. Or perhaps when one does, it is quickly killed off!

Of course, a behavioral change could prevent further spread: no bite, no cancer. Alas, for all the potential life saving benefits, behavior change is so hard. And that's true of both humans and Tasmanian devils.