tarry stools (a symptom of ulcers, which can be caused by mast cell tumors) Decreased or loss of appetite Difficulty breathing, urinating or defecating Types of cancer Dogs can develop many of the same types of cancer as humans. Many canine cancers are described with the same terminology and use the same classification systems as human cancers. Mast cell tumors are the most common type of skin cancer in canines. Lymphoma Prostate cancer Brain cancer Hemangiosarcoma is a type of cancer that develops almost exclusively in dogs, the only two other species known to have it are cats and horses. Hemangiosarcomas are tumors that form on the blood vessels, and can occur all over the body. These tumors can develop on the skin, subcutaneously, or on a blood vessel within an organ and are highly malignant. The tumors are most fatal when they rupture, causing the dog to suffer from severe loss of blood, or hypovolemia. Dogs are one of three mammalian species that are known to suffer from a transmissible cancer. Canine transmissible venereal tumor (CTVT) is species specific and highly contagious. The cancerous cell lines are transmitted between individuals that are in close contact with each other through acts of intercourse, biting, scratching, or licking. The cancer is prevalent in populations of stray dogs or environments of uncontrolled copulation. The tumors occur around the area of external genitalia and can grow up to 15 cm in area. Canine transmissible venereal tumors can often be infected, ulcerated, and hemorrhagic. Susceptibility Cancer prevalence in dogs increases with age and certain breeds are more susceptible to specific kinds of cancers. Millions of dogs develop spontaneous tumors each year. Boxers, Boston Terriers and Golden Retrievers are among the breeds that most commonly develop mast cell tumors. Large and giant breeds, like Great Danes, Rottweilers, Greyhound and Saint Bernards, are much more likely to develop bone cancer than smaller breeds. Lymphoma occurs at increased rates in Bernese Mountain dogs, bulldogs, and boxers. It is important for the owner to be familiar with the diseases to which their specific breed of dog might have a breed predisposition. A study of 144 female dogs found that dogs eating higher amounts of red meat, especially beef and pork, were more likely to get mammary cancer. Treatment Treatment options vary and depend on the type and stage of cancer. Common treatments include surgery, chemotherapy, radiation therapy, amputation,