Does Chemo Shrink Bone Cancer in a Dog?

Bigger dogs are more likely to develop osteosarcoma.
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Bone cancer in dogs can be one of the most difficult ailments to treat effectively. The most common form of canine bone cancer is osteosarcoma; it accounts for 85 percent of all cases. Unfortunately, once a dog is diagnosed with osteosarcoma, the cancer has already moved into other parts of the body in 90 percent of cases. A combination of treatments, including chemotherapy, serves to treat the cancer and to prolong the life of an affected dog.

Bone Cancer & Osteosarcoma

As the name suggests, bone cancers are those that start developing in the bones. These cancers tend to affect older and larger dogs at a higher rate than younger and smaller dogs. According to the American Kennel Club's Canine Health Foundation, dogs who weigh more than 90 pounds account for one-third of all cases of canine bone cancer, and the median age of diagnosis is 8 years or older. The foundation estimates that 10,000 cases of this type of cancer are diagnosed annually. Osteosarcoma is the most common, and one of the most aggressive, forms of bone cancer affecting dogs. According to the National Cancer Society, osteosarcoma begins in the bone cells. Tumors associated with the cancer are found most frequently on the lower part of the dogs’ front limbs, usually closer to the paws.

Treatment Options

Because osteosarcoma is an aggressive form of cancer, it spreads quickly into other organs. By the time a dog has been diagnosed, the cancer has usually metastasized or spread. To slow the spread of the cancer, chemotherapy is usually administered. Because bone tumors are painful, veterinarians typically amputate a dog’s affected limb. This amputation can help stop the cancer from spreading if it has not metastasized already. Radiation can also be used, especially in cases when amputation is not recommended. For example, dogs who have severe arthritis in their limbs may not be good candidates for amputation.

Role of Chemotherapy

Chemotherapy involves the use of cytostatics, drugs designed to stop cells from dividing and multiplying. The U.S. National Library of Medicine describes four goals of chemotherapy: to eliminate all of the cancer cells from the body, to eliminate the cancer cells that remain in the body following surgery, to reduce tumors before surgery and to reduce side effects or slow the spread of the cancer. In the case of canine bone cancer, chemotherapy is most often used following surgery to remove the rest of the cancer and to slow the spread of the cancer so the dog may live comfortably for a little longer. Because most bone tumors are removed by amputating the entire limb, chemotherapy is not usually used to reduce the size of the tumor.

Radiation Option

If a dog is not a good candidate for amputation, veterinarians may attempt to reduce the size of the tumor and increase the dog's comfort using radiation. According to the National Cancer Institute, radiation therapy helps shrink tumors so the pressure and the pain resulting from that pressure are relieved in the patient. This form of treatment uses high doses of radiation to kill the cells and to stop them from multiplying.