Fortunately, testicular cancer rarely spreads in dogs, unlike in human beings, so treatment has a high success rate. As in humans, animals that receive excessive exposure to sunlight are at risk for skin cancers, but only in animals or areas without hair or pigmentation. For cats, risk areas include the pink tip of the nose, the eyelids, and areas around the ears. For dogs the risk is associated with a fair complexion and exposure to the underbelly or inside of the back legs. In high mountain areas where ultraviolet light is particularly strong, skin cancer often affects pointers, bull terriers, pit bulls, and Dalmatians.
Dogs have a much higher incidence of nasal sinus cancer than do people.
Carcinogens range from herbicides and pesticides for dogs in rural areas to factory or automobile pollution for urban dogs. The mouth is the fourth most common site of cancer in domestic animals. It may be that mouth cancers arise at such high frequencies in dogs and cats because carcinogens from the air land on their coats and get into their oral tissues when they groom them-selves. Breeds with dark pigment in the mouth, such as German shepherds, black cocker spaniels, Scotties, and chows, are prone to melanoma in the mouth. Swelling around a tooth when there is no tooth injury or dental disease could be a sign of mouth cancer.