Pet dogs are a powerful natural model system for cancer and other human diseases. The importance of dogs for comparative and translational cancer research continues to grow because they overcome limitations inherent in other model systems (1-3). Dogs spontaneously develop many of the same cancers as humans, with clinical, pathological, and genomic similarities to human cancers (2). They develop these cancers while sharing our environment and in the context of an intact immune system. The clinical course of dog cancers is often accelerated, reflecting their shorter lifespans. As a result, clinical trials in pet dogs can be performed more quickly and with more flexibility than in humans, and benefit both dog and human cancer patients.