Diagnosing Bone Cancer (Osteosarcoma) in Dogs
Osteosarcoma is preliminarily diagnosed on the basis of a dog’s history, a thorough physical examination and X-rays (radiographs) of the suspected affected areas of bone. If osteosarcoma is present, the X-ray films will show aggressive bony lesions characterized by a moth-eaten, ragged appearance. Osteosarcoma is a very aggressive form of cancer. It almost always spreads quickly through the blood stream and lodges in remote places in the dog’s body – especially in the lungs. This is referred to medically as “metastasis.” Once bone cancer is identified, the veterinarian will probably recommend taking X-rays of the dog’s chest, to assess whether the cancer has spread from bone to the lungs. When analyzing these films, the veterinarian will be looking for one or more hazy but fairly distinct whitish patches throughout the tissues of one or both lungs. Actually, the doctor will hope not to find these shadowy patches on the
X-ray films. Unfortunately, roughly 95% of dogs with osteosarcoma will ultimately have their cancer spread to their lungs or to other areas of their bodies, even if their primary bone tumors are surgically removed.
The initial medical database probably will also include a urinalysis and routine blood work (a complete blood count and a serum biochemistry profile). The results of these tests will help the veterinarian rule out a number of other possible causes of the dog’s symptoms. However, a definitive diagnosis of osteosarcoma requires microscopic evaluation of tissue samples taken by surgical biopsies of affected bony areas. Depending upon the location of the tumors and the owner’s willingness to treat the condition aggressively, the attending veterinarian may suggest surgically removing the entire mass, along with quite a bit of the surrounding tissue, to get diagnostic samples, and hopefully at the same time to possibly remove most or all of the cancerous bone cells. Because most cases of osteosarcoma start in one of a dog’s legs, removing the cancer typically is attempted by partial or total amputation of the affected limb. The biopsy sample, or the part of the leg that was surgically removed, will be sent to a medical laboratory for evaluation by a veterinary pathologist who will be able to identify the exact kind of cancer that is present.
If the attending veterinarian suspects that her patient has osteosarcoma in places other than its legs, a computed tomography scan (CT scan) will probably be advised. The detailed images produced by a CT scan can help the doctor assess the severity and spread of the cancer and plan surgery, radiation, chemotherapy or other forms of therapy. CT scans are highly specialized diagnostic procedures that require expensive medical instruments and well-trained personnel. They usually are only available at veterinary teaching hospitals and some referral centers.
Chondrosarcoma, which is the second-most common form of primary bone cancer in dogs after osteosarcoma, usually affects the ribs, pelvic bones or muzzle rather than the long bones of the legs. Chondrosarcoma typically shows up in middle-aged dogs as a large, hard, painless mass in an area where cartilage is present. Cartilage is a gristly type of connective tissue that provides the matrix or framework upon which bone is formed. In dogs, chondrosarcoma is much less aggressive than osteosarcoma.