Osteosarcoma in dogs

For several months, we are looking at cancer in dogs. This is by far the most common disease I see in my end-of-life specialty practice. We see all types of cancer ó most of the same ones seen in human oncology.One of the most devastating is cancer of the bone ó osteosarcoma. It is most commonly seen in the long bones of the limbs but can develop in the bones of the skull, spine or rib cage; and there are rare cases of this tumor arising in non-boney tissues like mammary glands and muscle.It is most commonly found in large or giant breeds of dog. There are several scientific papers that correlate the development of this tumor with the weight and height of dogs, and it is well-known that certain dog breeds develop this tumor more often than others.The cancer is extremely painful and the usual first complaint for these dogs is lameness, which may respond to standard doses of painkillers initially but rarely for more than a week or so. At this time, a swelling in the bone at the site of the tumor might be noted ó this is often painful, red and hot to the touch; however, it may present only as a bump on a leg bone with no pain.Osteosarcoma spreads rapidly. Experts say that by the time this cancer is diagnosed, 80 percent of cases have micro-metastasis. Consequently, any treatment plan must address the secondary spread of the cancer as well as the primary tumor itself.The first step is to get some plain radiographs of the affected site. While some osteosarcomas in dogs cannot be definitively diagnosed on X-rays alone, a presumptive diagnosis can often be made; and, in many cases, a biopsy is not necessary. In addition, X-rays of the lungs are taken to rule out the presence of metastasis in the lungs.The management of this disease must focus on both the primary and the secondary tumors and or the metastasis.The ideal therapy would involve complete removal of the primary tumor, and this most often requires amputation. Many dogs do very well following amputation, but clearly there are some dogs for whom this would be inappropriate. If the dog also has neurological problems or severe arthritis or would not do well with a front leg amputation, then amputation surgery might not be a good idea. Amputation is tolerated well by many dogs; if done early, it might help the dog live longer than the average survival time. However, it is no guarantee that other spots of this cancer will not show up elsewhere.Chemotherapy is often used in conjunction with amputation. There are also schedules for radiation in conjunction with chemo. Radiation is very difficult as it requires sedation or anesthesia of the dog for each treatment ñ- and they will need many. The cost and complexity make it often not practical. Success all depends on how early any of these attempts can be started. Because of the fast rate of spread, it is often a disappointing treatment.Sadly, the development of metastatic secondary cancer leads to euthanasia of many dogs with osteosarcoma. There are new therapies being tested for this devastating cancer; so far, there is no good evidence of an improvement in outcome associated with these treatment protocols.Here are the important facts if your dog gets a diagnosis of osteosarcoma. Without therapy, the average survival time from diagnosis is about two months. This is primarily determined by the discomfort associated with the primary tumor. If amputation is performed, the average survival time is about six months with only 2 percent of patients living after two years. Amputation with chemotherapy makes the average survival time just less than one year, with less than 20 percent of dogs still enjoying a good quality of life two years after surgery. With all the chemo and radiation, dogs have an average life expectancy of six months ó that is how devastating this cancer is.I lost my dear Great Dane, ìTaylor,î a few years ago to this devastating cancer. We did everything that Colorado State University could offer. Looking back, I feel we put her through so much only to have her die about a year after diagnosis. Iím not sure I would do that again.More advances need to be made in the amputation and chemotherapy protocols for this to become a practical option.