How Osteosarcoma Affects Dogs
Osteosarcoma frequently affects the upper or lower long bones of a dog’s front legs. These are called the humerus, and the radius and ulna, respectively. The long bones of the rear legs can be affected, as well; these are the femur, tibia and fibula. The jaw and other facial bones, as well as the ribs and vertebrae, can also be subject to osteosarcoma. The first sign of osteosarcoma usually is a slight but progressive limp in an adult dog that has no prior history of trauma or injury. Over time, the areas where the bone tumors are located will become swollen, hard and extremely painful.
Symptoms of Bone Cancer
Dogs suffering from osteosarcoma may develop one or more of the following symptoms, depending upon the location and maturity of their bone tumors:
- Lameness; progressive and of varying severity; the dog may be non-weight-bearing on the affected leg; limping is typically noticed by the owner of a mature dog with no history of leg trauma
- Pain (often severe)
- Swelling around the affected area of the leg; most often evident in one leg rather than several; usually painful
- Broken bones at the tumor site (called “pathologic fractures”); caused by bone weakness from the cancer; usually no history of physical injury to the area
- Swollen upper jaw (maxilla); usually painful
- Swollen lower jaw (mandible); usually painful
- Pain when opening the mouth
- Nasal discharge
- Swelling and pain along the spine
- Swelling and pain around the ribs
- Difficulty eating or chewing (dysphagia)
- Lack of appetite (inappetence; anorexia)
- Respiratory distress (difficulty breathing; dyspnea); typically caused by rapid spread [metastasis] of the cancer from bone to lung tissue; can also be caused by osteosarcoma of the ribs)
Dogs at Increased Risk
Osteosarcoma is basically a disease of middle-aged and older dogs, with the average age of onset being about 8 years. Males and females are equally at risk. Large and giant breed dogs are predisposed to developing this type of cancer, although the reasons for this association are not well-understood. The Saint Bernard, Newfoundland, Great Dane and Great Pyrenees are reported to be 60 times more likely to develop osteosarcoma than are dogs that weigh less than 65 pounds. Large breed dogs, such as the Irish Setter, Golden Retriever, Labrador Retriever and Boxer, reportedly are about 8 times more likely to be affected by osteosarcoma than are smaller dogs. Toy breeds rarely develop this type of bone cancer.
A dog’s height and weight are more closely associated with its chances of developing osteosarcoma than is its breed. Larger animals usually develop osteosarcoma in only one of their legs. Smaller dogs can develop osteosarcoma in their legs, but they are equally likely to have this form of cancer show up in other parts of their skeleton.