Canine osteosarcoma usually appears in large dogs, often in the legs. Sometimes the tumor originates in a place where an earlier injury occurred. Warning signs include limping, especially progressive lameness, and swelling. The cancer weakens and destroys the bone as it progresses, which can sometimes result in fractures.
This is a primary tumor, which means that the cancer originates in the bone and then moves elsewhere in the body. It is extremely aggressive. The cancerous cells tend to metastasize first to blood-rich cells, such as those present in the lungs. Frequently, by the time the dog manifests visible symptoms, such as limping or swelling, the cancer has already spread. Repeated coughing is a sign that it may have invaded the dog’s lungs.
Treatment options include surgery, radiation therapy, and chemotherapy. The traditional surgical option is amputation, but recently a few universities have been performing limb-sparing procedures. This usually involves removing the tumor and strengthening the limb with a bone graft. Whatever surgical option is chosen, it must be combined with chemotherapy and/or radiation therapy in order to be effective. This is because surgery removes the main tumor, but if the cancer has metastasized to the lungs or spread elsewhere in the bones, it will only continue to advance.
Chemotherapy is very effective at killing any remaining cancer cells present in the dog’s body. Basically, it is the process of injecting or administering orally a combination of drugs designed to target cancer cells. Chemotherapy drugs kill cells that grow quickly, like cancer cells. (Other fast-growing cells include those in the hair follicles, which explains why chemotherapy can cause hair loss.) The idea is to kill the cancer cells without permanently damaging other, healthy ones.
Both chemotherapy and radiation therapy can be offered in lieu of surgery. This is good, because some dogs are not good candidates for surgery, such as those who are elderly or suffering from hip dysplasia or arthritis. But if chemotherapy and radiation therapy aren’t appropriate either, then pain management becomes paramount.
Veterinarians have a wide range of narcotics available to control pain, many of which are also approved for use in humans. As with humans, however, these drugs may inhibit a dog’s responses. He or she may sleep too much, or seem woozy or dazed. If this is the case, the veterinarian may suggest delivering the narcotic through the dog’s skin, in the form of a patch. This method has risks of its own, but can significantly enhance the quality of the dog’s life.