Diagnosing Osteosarcoma in Dogs

With over 10,000 cases diagnosed each year of osteosarcoma, dogs need to be monitored carefully for any sign of lameness. Highly aggressive and painful, osteosarcoma is a very common form of cancer appearing in dogs, primarily affecting middle-aged large and giant purebred dogs. Dogs weighing more than 80 pounds are 60 times more susceptible than dogs weighing 75 pounds. It is also more common in males.

Osteosarcoma or dog bone tumor cancer accounts for 80-90% of all malignancies involving the bone, yet it accounts for only 5% of all canine bone cancer tumors. Often requiring amputation of the affected limb coupled with chemotherapy for temporary relief, this cancer can produce lameness relatively quickly. Unfortunately, by the time the tumor is discovered in the limb, the cancer has already spread.

Symptoms of Osteosarcoma in Dogs

Canine bone cancer manifests itself as lameness in the affected limb. Starting intermittently and progressing in permanency as the tumor grows and damages more of the bone, lameness is also the result of the increase in pain, swelling and the formation of the tumor.

Osteosarcoma is most prevalent to the bones of the limbs (appendicular osteosarcoma) away from the elbow and close to the knee or in the "wrist" or shoulder, accounting for 75 to 80% of the cases. However, it can also affect the bones of the spine, ribs or skull.

Originating deep within the bone, the tumor grows outward, destroying bone from the inside out and replacing it with tumorous bone, becoming increasingly more painful. Minor injuries can actually cause bone fractures since tumorous bone is weaker than normal bone. These pathologic fractures do not heal.

Treating Canine Osteosarcoma

A physical examination, X-rays of the bone and lungs, blood work, and a biopsy is needed to indicate whether osteosarcoma is present since other bone tumors, as well as fungal or bacterial infections, can cause the same lesions. Lung x-rays will determine if the cancer has spread. Dog often will cough or gag when the cancer has spread to the lungs, which occurs in approximately 90% of all new diagnoses.

Limb-sparing procedures, such as a bone graft, may be an option; however, usually only amputation is the only treatment available. Limb-sparing procedures can only be done in cases where no more than 50% of the bone is involved, the tumor is located at the lowest part of the leg and when no muscles are involved. Bone implant rejections and fractures can complicate recovery. By removing the tumor, the source of pain and the source of spreading the cancer is eliminated. Radiation therapy is sometimes necessary to control the pain.

Chemotherapy After Amputation

Chemotherapy is usually done immediately after amputation to reduce the possibility of the spread of the tumor and to relieve pain. Recovery from surgery and the adaptation to life as an amputee is usually event free and quick. Carboplatin and cisplatin are the most successful drugs available to date; however, carboplatin is more expensive but the safer one to use. Doxorubicin is sometimes combined with cisplatin. The selection of medications depends upon each medications' advantages and disadvantages. Pain relief is found with gabapentin, tramadol, amantidne or a non-steroidal anti-inflammatory (NSAID) medications such as deramaxx, rimadyl, metacam, or etogesic or a combination of these drugs.

Some survivors live a year or longer; however, the median survival rates vary but are often less than one year.