My ears always perk up when my professors start saying really strange stuff. So when I heard Dr. Levine say, "Now if you are interested in X-files type fringe stuff..." I listened! He was referring to Canine Venereal Tumor (aka Transmissible Venereal Tumor, Sticker Tumor or Infectious Sarcoma). This strange cancer is spread by contact-- cells of the cancer are directly transferred from one dog to the next by touch! It is considered an STD-- I bet you didn't know that animals can get STDs as well as people-- although it can also be passed by one dog sniffing another's genitalia, in which case it infects the nasal cavity.
Another really weird thing about this cancer is that it can be traced back to a single animal, probably an Asian wolf, living about 200 years ago! There are several pieces of evidence for this-- all CVT tumors have very similar genetic make-up, but contain less chromosomes than a dog and have chromosomes of a different shape than dog chromosomes (their centromeres are positioned differently). Also, there is no viral component to this cancer. The analysis used to determine where this cancer originated involved a group of 16 dogs in three different countries-- Italy, India and Kenya-- as well as another 400 dogs from 85 different breeds, and was the published by Claudio Murgia in Cell in 2006.
The age of this cancer means it is one of the oldest cancers in the world. Interestingly, it was first identified over 100 years ago, in 1876, by a Russian veterinarian who showed that tumor cells from one dog could be used to infect another dog.
The cancer is found in many parts of the world, mainly in warm climates. It can be passed to other canids, including coyotes and foxes.
CVT is a histiocytic cancer, meaning its lineage is derived from the same lineage as macrophages. It forms cauliflower shaped tumors. Signs of genital infection include discharge and difficulty urinating due to blockage by the tumor; signs of nasal infection are also discharge, as well as nosebleed, oronasal fistulae and facial swelling.
Interestingly, CVT appears to have become less aggressive with time. It often regresses on its own after a period of several months, and rarely metastasizes. If it doesn't regress, the standard treatment is systemic chemotherapy (at Cornell: vincristine, 2 treatments past gross resolution of the disease) or radiation therapy.
The only other known transmissible cancer is a sad story. Devil's Facial Tumor Disease infects Tasmanian devils (an Australian marsupial) and is the main factor contributing to their being endangered as a species. You can read more about it in
this New York Times article from Dec 31, summarizing the recent findings of a Science paper on the subject.