Osteosarcoma is by far the most common bone tumor of the dog, usually striking the leg bones of larger breeds. Osteosarcoma usually arises in middle aged or elderly dogs but can arise in a dog of any age with larger breeds tending to develop tumors at younger ages. Osteosarcoma can develop in any bone but the limbs account for 75-85% of affected bones. Osteosarcoma of the limbs is called “appendicular osteosarcoma.” Osteosarcoma develops deep within the bone and becomes progressively more painful as it grows outward and the bone is destroyed from the inside out. The lameness goes from intermittent to constant over the period of mere months. Obvious swelling becomes evident as the tumor grows and normal bone is replaced by tumorous bone. Osteosarcoma is unfortunately a fast spreading tumor. By the time the tumor is found in the limb, it is considered to have already spread. (Osteosarcoma spreads to the lung in a malignant process called “metastasis.”). Prognosis is substantially worse if the tumor spread is actually visible on radiographs in the chest so if chemotherapy is being contemplated, it is important to have chest radiographs taken. Young dogs with osteosarcoma tend to have shorter survival times and more aggressive disease than older dogs with osteosarcoma. While osteosarcoma of the limbs is the classical form of this disease, as mentioned above, osteosarcoma can develop anywhere there is bone. “Axial” osteosarcoma is the term for osteosarcoma originating in bones other than limb bones, with the most common affected bones being the jaws (both lower and upper). Victims of the axial form of osteosarcoma tend to be smaller, middle-aged, and females outnumber males 2:1.
Causes
There are various reasons why osteosarcoma in dogs can occur. Some family lines simply have a genetic predisposition to this cancer. Other dogs may have pre-existing abnormalities. Other common reasons include radiation, chemicals, and foreign objects such as bullets or metal implants.
Symptoms
As mentioned earlier, this cancer grows deep inside the bone and progresses outward. As the condition advances, your dog will experience more pain. The affected limb will swell up and become lame. In its early stages, this period of lameness will only occur occasionally. Over time, it will affect your dog constantly.
Diagnosis
If your dog shows any of these symptoms of canine osteosarcoma, you should have him checked out as soon as possible. The first step will be to take an x-ray of the limb. This is usually the only procedure necessary. In some cases, a biopsy of the bone will be done to provide a definitive diagnosis. However, this is usually avoided due to the pain involved.
Treatment
Osteosarcoma in dogs needs to be treated as soon as possible as the tumor spreads rapidly. Medication will be prescribed to try to control the growth of the tumor. Your dog will also need medication to control pain. It may be necessary to remove the affected limb if your dog starts experiencing too much pain and statistics are in their favour with age/breed/stage of Cancer diagnosed being taken into serious consideration. Radiation and chemotherapy are also possible treatment methods with or without leg amputation and also should be based upon the same factors I listed above.
Author: Gwendilin Boers