Canines are in a rare category when it comes to cancer: They and Tasmanian devils are the only two animals that can transmit it from one individual to another.

A new genetic study reveals that the dog form of the cancer, which causes genital tumors, is 11,000 years old—making it the oldest continuously living cancer.

Canines can also develop cancers that are akin to human cancers, but their transmissible cancer spreads when cells from one dog's tumor rub off during sexual contact and grow into a new tumor on the other animal. The study notes that the cancer originated in an ancient dog closest to the modern-day breeds of Alaskan malamutes and huskies.

We spoke with Elizabeth Murchison, the study's first