Debbie Lindsey shared this: http://www.npr.org/blogs/health/2014/01/23/265236618/contagious-cancer-in-dogs-leaves-prehistoric-paw-prints?utm_content=socialflow&utm_campaign=nprfacebook&utm_source=npr&utm_medium=facebook
Murchison and her colleagues found that the infectious cancer is a living fossil. The modern tumors contain the DNA of an ancient pooch that hung out with prehistoric people thousands of years ago.
According to the comments that follow (verification is needed), the two transmissible cancers in dogs are the TVT (the transmissible venereal tumour that we often hear about and have seen) and the Tasmanian Devil Facial Tumour.
Another article: http://www.medicalnewstoday.com/articles/271646.php
About clonally transmissible cancers in dogs and Tasmanian Devils: http://www.nature.com/onc/journal/v27/n2s/abs/onc2009350a.html