Dogs, as well as other companion animals, stricken with cancers are being treated and studied, in part, to pursue advancements that could lead to cancer cures in treating humans. Medical doctors, veterinarians and researchers are working together in hope of better understanding, and treating, cancers that link pets and people. The cooperative approach, known as comparative oncology, is the focus of a new documentary, “The Answer to Cancer May Be Walking Right Beside Us,” produced by Colorado State University and Rocky Mountain PBS, which airs at 9 p.m.