Osteosarcoma, a bone tumor, is one of the most rapidly metastasizing -- or spreading -- of canine cancers. Approximately 90 to 95 percent of these tumors have already spread by the time the dog is diagnosed, according to Washington State University College of Veterinary Medicine. While you probably can't save your dog's life, certain treatments help alleviate the severe pain and can extend his time with you.
Osteosarcoma tumors develop deep within a dog's bone, usually but not exclusively in a limb. The tumors destroy bone from the inside out. Initial symptoms include sudden lameness or a lump on a leg. Sometimes, the first indication of a problem is a broken limb that occurring without serious trauma. While osteosarcoma in a limb grows rapidly, that's not the case with axial osteosarcomas, which generally appear in the jawbones. It can take two years or more for jawbone tumors to develop and significant symptoms appear. Unlike classic osteosarcoma, jawbone tumors often affect smaller dog breeds.
Although osteosarcoma can strike any dog, it's much more common in larger breeds. Any dog weighing over 80 pounds is at significantly increased risk. Susceptible breeds include the Great Dane, Saint Bernard, Irish wolfhound, boxer, Doberman pinscher, Rottweiler, German shepherd, Labrador retriever, golden retriever, Weimaraner, Newfoundland, Great Pyrenees and Bernese mountain dog. Males are more often affected than females. While the majority of osteosarcoma is diagnosed in older canines, it's not uncommon for large-breed dogs age 2 and under to develop the disease.
To make a definite diagnosis, your vet performs a bone biopsy or fine needle aspirate to collect a tumor sample. If the tests prove positive for osteosarcoma, your vet will X-rays your dog's lungs or perform an abdominal to check for metastasis.
Because the tumor causes pain, your vet might recommend amputating the affected limb. If the tumor has already spread, this won't cure your dog, but getting rid of the leg eliminates a major pain source. Most dogs function relatively well on three legs. Your dog might also receive radiation and chemotherapy to treat the cancer, along with pain medication. If the pain becomes too great and medication is no longer sufficient, most owners opt for euthanasia.
Because osteosarcoma spreads so quickly, the long-term prognosis for all but that small percentage of dogs whose tumor had not spread by the time of diagnosis isn't good. According to the University of Florida College of Veterinary Medicine's website, leg amputation and radiation might buy your dog three to four months of good quality time before further metastasis, with chemo adding up to a year. Approximately 20 percent to 25 percent of treated dogs will be alive two years later.