Bone tumors, a cancerous bone condition medically known as osteosarcoma, now afflicts about 8 out of every 10,000 U.S. dogs annually. Large and tall breeds, as well as older dogs, are more likely to develop osteosarcoma than small breeds. Although the exact cause of this cancerous condition is not known at this time, most medical researchers suspect osteosarcoma is probably a genetically predisposed disease.
In its active stage, osteosarcoma (OSA) is very painful and destroys localized bone tissue, causing the affected bones to become weakened, thereby dramatically increasing the risk of spontaneous bone fracturing. OSA affects a dog’s legs about 75% of the time, and front legs are twice as susceptible than hind lags. Initially, the most common area where osteosarcoma is detectable is in the radius bone, but OSA usually spreads very rapidly and has a high metastasis rate. Left untreated, most dogs succumb to the disease within 2 months after OSA’s symptoms appear.
The initial problem prior to diagnosis is often lameness and/or pain associated with a recent mild trauma. Many times this pain is misdiagnosed as a strain or sprain. During radiograph tests, the affected area often shows as lytic, or otherwise eaten away bone tissue, and the lesion often has a sunburst appearance.
Before treatment is started, a complete workup is necessary to determine if the dog’s cancer has spread and to determine the general health of the dog and its ability to withstand treatment. This could include a complete blood count, serum chemistry profile, urinalysis, thoracic, abdominal and expansile radiographs, radiographs of the appendicular skeleton and, if possible, a nuclear bone scan. A biopsy obtains a core of bone and is usually done under general anesthesia. This sample is examined microscopically to determine the cell type and to reach a correct diagnosis.
The treatment of choice for OSA is surgery followed by chemotherapy. The goal of treatment is to increase the dog’s quality of life, to lengthen its lifespan, and to decrease pain. This is achieved through control of the primary tumor as well as by slowing the cancer’s metastasis. Unfortunately, curing the disease is not truly a reasonable goal and is only attained about 10% of the time. The average length of remission is about 1 year, but can be longer in some dogs.