Info Sheets

An osteosarcoma is a cancer of the bone. It usually arises in the bones of the limbs but can develop in the bones of the skull, spine or ribcage and there are rare cases of this cancer arising in non-bony tissues like mammary (breast), internal organs, or the eye. Osteosarcoma is the most common primary bone cancer in cats, but it remains rare. There is no known breed or sex predilection. It mostly develops in middle aged cats, but rare cases have been reported at a young age.

©David Godfrey

Osteosarcoma of the limb bones can be extremely painful and the typical presenting complaint for affected cats is that of an intermittent lameness and bone swelling. The lameness may respond to standard doses of painkillers initially, but rarely for more than a week or so. Sometimes a swelling in the bone at the site of the cancer may be noted and this is often painful, red and hot to the touch. Rarely, a pathologic fracture, where the bone breaks because it is too weak due to cancer, may occur and non-weight baring lameness with severe acute pain would develop. If the cancer affects non-limb areas, clinical signs such as paralysis (when the cancer develops in the spine), a mass on the head (when the cancer develops in the skull), or difficulties breathing (when the cancer develops in a rib) may be noticed.

If your veterinarian suspects that your pet has a bone cancer they will first want to take X-rays or a CT scan of the affected site. Whilst osteosarcoma cannot be definitively diagnosed on imaging alone, a presumptive diagnosis can be made, and in some cases biopsy is not necessary. However, when the bone is severely destroyed, a needle can be inserted in the area that is suspicious of cancer to obtain a cell sample. In addition, X-rays or CT scan of the lungs are obtained to see if the cancer has spread. If there are any other painful bone lesions these should be investigated as osteosarcoma can spread to other bones. If your veterinarian detects any enlarged lymph nodes in the region of the bone lesion samples can be taken using a needle and syringe to collect a few cells for examination.

The most pressing concern in patients with osteosarcoma is undoubtedly the pain associated with the bone cancer. It is also important to be aware of the fact that osteosarcoma in cats may spread to the lung, which has been reported in 10 to 45% of cases. Therefore, any treatment plan should be set after staging, as the presence of metastatic disease may be a contraindication for local treatment. Treatment of the primary tumor The ideal therapy involves complete resection (removal) of the bone cancer and this most often requires limb amputation. Most cats cope extraordinarily well following amputation, but rarely there are some patients for whom this would be inappropriate. Concurrent neurological problems or severe arthritis are reasons for not considering amputation. Moderate arthritis can be managed extremely well with suitable medication and need not be a reason for rejecting amputation; obviously this should be evaluated on a case-by-case basis. Amputation invariably has a tremendous impact on the state of mind of the patient. While it is clearly a major operation, these patients seem to be so relieved to be free from the pain that they recover extremely quickly. When the cancer develops in a non-limb location, such as the spine or the skull, surgery may be more challenging due to anatomical constraints, and it is not always possible to remove the whole cancer. In these cases, radiotherapy may be considered to complete treatment and treat the cancer cells that have remained in the body. For the patients in which amputation is not appropriate, palliative therapy can be administered in the form of radiotherapy (weekly for 4 weeks or as a quad shot over 2 consecutive days) and possibly chemotherapy. Other radiotherapy treatment protocols are described, and this is an active area of research, so it is worth consulting a radiation oncologist if further detail is required. A drug called bisphosphonate, that helps to slow down bone destruction, and strong pain relief are recommended alongside radiotherapy in the palliative setting. Treatment of secondary spread In cases that present with metastatic disease, ie when the cancer has already spread to the lungs, chemotherapy may be attempted in the palliative setting. As a rule, this treatment is tolerated extremely well. The most widely used chemotherapy protocol involves treatment once every three weeks for a total of four to six doses. With the constant emphasis on quality of life, most oncologists choose to use chemotherapy aiming for reduced side effects whilst maintaining the same beneficial results in terms of cancer control and overall survival. In most cases, chemotherapy treatment passes uneventfully. It is important to fully discuss with your vet all the risks of chemotherapy administration prior to embarking on a course of treatment.

Following diagnosis, life expectancy for osteosarcoma of the limbs has been reported between a year and several years. Life expectancy for osteosarcoma in the other bones is shorter due to difficulty of achieving complete surgical removal, with an average survival around 6 months reported.