In last month’s issue, we discussed lymphoma, one of the most cancers seen in both dogs and cats. The next tumor, however, is primarily seen in large dogs, only occasionally in small dogs and very rarely in cats.
Osteosarcoma, a type of bone cancer, is most commonly found in the radius (lower front leg) just above the carpus, or wrist joint. Next most common is the top of the humerus (upper front leg), then the back leg just above or below the knee, followed by other bones such as the scapulae, pelvis and even vertebrae and toes. Dogs present with a limp that gets worse and sometimes swelling of the bone is seen. The bone will be painful when it is squeezed — a big hint that there may be a serious cause of the lameness. An x-ray will usually show abnormal bone in that area. Sometimes a biopsy is necessary, but often we can be confident with the diagnosis just by the exam and x-ray. Unfortunately, osteosarcoma is very painful and also very quick to spread. Non-steroidal anti-inflammatories such as Rimadyl or Deramaxx can control the discomfort for a while and may actually slow the growth some, but eventually they are not enough.
To give these dogs as long and as good a quality of life as possible, surgery is indicated. It may sound drastic, but amputating the limb is the best course of action. Dogs can do quite well with just three legs. They learn to shift the single leg towards the center to balance themselves. The most important thing is that once the surgery site heals, the source of their pain is gone. It is amazing to see how happy these dogs are just days after their operation. However, although the pain is relieved, the tumor has almost always started to spread and is usually seen in the lungs within 2-6 months. Another option after surgery is to do chemotherapy. It is a much less rigid protocol than the one for lymphoma and is comprised of just one drug, carboplatin, given once every three weeks for four doses. As far as chemotherapeutic agents go, it is not terribly toxic and can extend a pet’s life an additional six to twelve months.
Part of the evaluation of a dog with osteosarcoma is to get bloodwork and chest x-rays. We look at the chest for evidence of metastasis (spread). On the bloodwork, we pay particular attention to an enzyme called alkaline phosphatase (ALP). This enzyme is usually associated with liver function, but it is also found in bone. When the levels are elevated, this is a poorer prognosis. After the pet’s treatment, we often track their bloodwork and chest x-rays to see how they are doing. The most important thing, however, is how the pets feels. We want to keep them as happy and healthy as we can for as long as we can. Our pets give us love and joy and we want to do the same for them.