Research into cancer in companion animals is teaching us how to fight human disease, writes Juan Pascual of Elanco. Each year, millions of pets are diagnosed with cancer, thought to be the main cause of mortality in dogs older than 10. Statistics show that one in four dogs and one in six cats will develop cancer during their lifetime. For pets, we know even less about the causes of cancer than we do for humans, but we do know that genetics and environment factors play an important role.