Many people are surprised to learn that just like in people, cancer in dogs is a real problem. An Italian study from the journal BioMed Central Veterinary Research estimated that out of every 100,000 dogs, 800 to 900 will develop cancer. Dogs older than 10 and purebreds are at increased risk compared to mixed breeds.
Cancer affects dogs in the same way that it affects humans: stealing quality of life and years away from our furry friends. However, many treatments are available and veterinary research continues to improve every dog's possibilities at a long and happy life. Learn how to spot the signs so that you and your veterinarian can give your pup the best possible care if he ever needs it.

Types of Cancer in Dogs
Cancer in dogs can affect any and every organ in the body. Dog tumors on the skin may be lumpy and obvious, but cancer in the chest, brain, abdomen or blood can be more difficult to identify. According to the American Animal Hospital Association (AAHA), the most common types of cancer in dogs include:
- Lymphoma: Cancer of the lymph nodes that attacks the immune system
- Hemangiosarcoma: Cancer of the blood vessels
- Mast cell tumor: Cancer that can develop almost anywhere in the body but is often visible as a skin lesion
- Melanoma: Aggressive skin cancer that can develop in the mouth, eyes or foot pads
- Osteosarcoma: Malignant bone cancer, most common in large dogs
- Mammary gland carcinoma: Cancer of the mammary glands that can often be prevented by spaying a female dog early in life
Signs of Cancer in Dogs
The signs of cancer in dogs vary with what system the cancer is attacking or arising from, and whether it is benign and solitary, or malignant and spreading to distant areas in the body. For example, a lipoma, a common benign tumor of fat cells, shows up as a soft, movable lump under the skin. Mast cell tumors, on the other hand, can show up as red, angry skin bumps that look like an allergic reaction. Hemangiosarcoma, a cancer arising from the cells that line blood vessels, can show up as skin tumors or can spread to the spleen (and in some cases originate in the spleen), causing it to become enlarged, lumpy and fragile.
Keep a close eye on your dog's behavior if you think he may be sick. Limping, a swollen leg or excessively licking a leg may indicate bone cancer, while cancer in the brain can cause abnormal behavior or seizures. Knowing what "normal" looks like for your pup's mouth, paws, neck and joints can also help you spot abnormalities. Melanoma, for instance, can show up as a dark spot in your dog's mouth or a swollen paw. The first sign of lymphoma is often a swollen lymph node or lymph nodes in the neck or knees, the AAHA writes.
Malignant cancer in dogs tends to cause unexpected weight loss, and that may be the only visible sign. If you are concerned that your pet might have cancer, call your vet and schedule a physical exam for your dog as soon as possible.