Mastiffs, Saint Bernards, Great Danes and bulldogs are more likely to be diagnosed with cancer at a young age than bichon frises, West Highland white terriers and American Staffordshire terriers, according to a study in PLOS ONE. Male dogs and dogs that have not been spayed or neutered are more likely to develop cancer at a young age than females or dogs that have been sterilized, and the study leaders recommend starting to screen most dogs for cancer at age seven and at-risk dogs earlier.