Our canine companions suffer from some of the same diseases that we suffer from, and sadly cancer is one of them. Neoplasia is one of the leading causes of death in dogs. The increasing rate of cancer diagnoses is no doubt due in part to the fact that our dogs are living longer with improvements in nutrition and health care. Nonetheless, any mass that is prominent or persistent should be evaluated for neoplasia.
Common Cancers in Dogs
Many different types of cancer occur in dogs. These include lymphosarcoma, osteosarcoma, soft tissue sarcoma, mast cell tumors, hemangiosarcoma, oral melanoma and mammary neoplasia, among others.
Lymphoma, also called lymphosarcoma, is a general term applied to malignant neoplastic disorders of lymph tissue. It is the most commonly treated systemic cancer in veterinary medicine. It is very aggressive, but if diagnosed early can be managed. It frequently involves multiple lymph nodes, the spleen, liver and other organs. In late stages of disease, the bone marrow can become involved. Without treatment, the prognosis is very poor.
Osteosarcoma is a type of malignant neoplasia that always involves abnormal production and proliferation of bone, usually in the long bones of large and giant breed dogs. It can also occur in any other part of the skeleton. It is the most common bone cancer in dogs, occurring usually in middle-aged to older dogs with no obvious gender predilection. Osteosarcoma is highly aggressive and normally presents with progressive lameness in an older large dog. Localized swelling at the tumor site may be seen. Surgical removal of the primary tumor via amputation is the most common treatment protocol. This, together with chemotherapy, can enhance the dog’s quality of life. Unfortunately, most affected animals will eventually succumb to the effects of either the primary cancer or of its metastasis.
Soft Tissue Sarcoma
Canine soft tissue sarcomas are a group of tumors which arise from connective tissue and are classified together because of their similar biologic behavior and recommended treatment. They include fibrosarcoma, hemangiopericytoma, malignant fibrous histiocytoma, nerve sheath tumor, neurofibrosarcoma, malignant schwannoma, leiomyosarcoma, rhabdomyosarcoma, liposarcoma, myxosarcoma, lymphangiosarcoma and synovial cell sarcoma. These tumors are common in middle-aged to older dogs and seem more common in larger breeds, although no evidence of direct genetic inheritance has been reported at the time of this article. Soft tissue sarcomas tend to show up spontaneously in dogs and appear as firm masses on the legs, mouth or chest often appearing to be on top of, or right under, the skin. The goal of treating soft tissue sarcomas is complete eradication by surgery and other therapies.
Mast Cell Tumors
Canine mast cell tumors (MCTs) are common, abnormal, neoplastic and usually benign accumulations of mast cells that form nodular skin tumors which, when the mast cells ultimately degenerate, release histamine and other substances that can cause or contribute to gastrointestinal (stomach) ulceration, cutaneous (skin) lesions (including pruritus/itchiness) and even systemic clinical signs. Mast cell tumors have the potential to become malignant and often metastasize to other sites. Therefore, they should always be treated immediately when they are found. Treatment options include surgery, radiation, chemotherapy and immunosuppressive steroid administration. The appropriate treatment protocol will depend upon the diagnostic stage of the tumor(s) and the veterinarian’s particular recommendations.
Hemangiosarcoma is a malignant, highly metastatic type of cancer that arises from the cells lining blood vessels. It is common in middle-aged to older dogs of either gender. It tends to affect the spleen, heart, liver and skin, but can spread anywhere. Surgical biopsy is the gold standard for diagnosing hemangiosarcoma, and the goals of therapy are to control metastasis and prolong survival in affected dogs.
Tumors of the mouth and throat (oropharyngeal tumors) are common in dogs and include malignant melanoma (the most common canine oral tumor), fibrosarcoma, squamous cell carcinoma and epulides. All of these tumors should be biopsied along with radiographic studies (x-rays or CT scans) to determine the type and extent of disease. Aggressive surgical removal with wide margins is the optical treatment for any of these oral tumors. Radiation may also be helpful. Specific breeds of dogs seem to be more prone to developing this form of cancer.
Mammary tumors (breast cancer) are the most common tumors affecting intact female dogs. More than 50% of all tumors in female dogs are reported to be mammary tumors -- 3 times more common than breast cancer in people. This type of cancer is most commonly seen in older females (9-11 years) who either have not been spayed or were not spayed until after their second heat cycle. Breast cancer seems more common in Toy and Miniature poodles, English springer spaniels, Pointers and German shepherds. It also appears to be diagnosed more frequently in obese bitches over 1 year of age and in bitches on high red-meat diets. Mammary tumors are thought to be caused in part by fluctuating hormone levels as intact females mature through their heat cycles. Approximately 50% of mammary tumors in dogs are malignant carcinomas, adenocarcinomas or sarcomas, while the other 50% are benign. If diagnosed early, surgical excision is the treatment of choice for mammary tumors. Chemotherapy may also be recommended.