The Top 5 Skin Cancer Types in Dogs, including Sun Protection for Cell Carcinoma. Cancer is the leading cause of death in dogs, and since early detection can be the deciding factor in the outcome, never ignore any lump or bump on your pet. Summer might be coming to a close, but that doesn't mean that our dogs are any less susceptible to getting skin cancer. Squamous Cell Carcinoma is a type of skin tumor that may be attributed to sun exposure and is the second most commonly diagnosed type of tumor in dogs, right after Mast Cell Tumors.