Common Signs of Cancer in Dogs
Drs. Foster & Smith Educational Staff

CANCER MOST COMMONLY OCCURS in older dogs, although cancer in younger dogs is not unheard of. Common canine cancers include bone cancer, lymphoma, and mast cell tumors.

BONE CANCER (Osteosarcoma)

Osteosarcomas account for only 5% of all canine tumors, but 80-90% of malignancies that involve the bone. Much more common in large breed dogs, osteosarcoma is an aggressive cancer of the bone that often requires amputation of the affected limb coupled with chemotherapy.

LYMPHOMA (Lymphosarcoma)

Lymphosarcoma is a common cancer of lymphocytes in dogs and can occur in the lymph nodes, spleen, liver, and other organs. The cancer can be aggressive but treatment with chemotherapy has been very successful in adding months, and occasionally years, to the dog’s life.


Canine mast cell tumors account for up to 20% of all skin tumors in dogs. While they often appear small and somewhat insignificant, they can be a very serious form of cancer in the dog. Some mast cell tumors are easily removed without the development of any further problems while others can cause life threatening disease. Proper identification and treatment are very important in controlling these tumors. In early 2010, look for a new drug by Pfizer called Palladia, a drug that may hold promise for certain canine mast cell tumors.

According to the American Veterinary Medical Association, the ten most common signs of cancer in dogs are:

  1. Abnormal swellings that persist or continue to grow
  2. Sores that do not heal
  3. Weight loss
  4. Loss of appetite
  5. Bleeding or discharge from any body opening
  6. Offensive odor
  7. Difficulty eating or swallowing
  8. Hesitation to exercise or loss of stamina
  9. Persistent lameness or stiffness
  10. Difficulty breathing, urinating, or deficating