Osteosarcoma is the most common type of bone cancer in small animals. Approximately 80% of bone cancers in dogs are due to osteosarcoma. It is a neoplasia of the osteoclast and osteoblast cells of the bone. These cells have the job of depositing minerals and building the bone. It is a cancer which rapidly grows and invades surrounding areas. It also spreads to other parts of the body very easily. There are other types of bone cancer which affect other types of cells within bones. These are chondrosarcomas, fibrosarcomas and synovial cell carcinomas- these conditions will not be discussed further in this article.
Osteosarcoma is commonly found in the long bones of the limbs such as the femur; it may also affect other bones such as the vertebrae or ribs although this is relatively uncommon. The first signs of a problem noticed by the dog's owner is often lameness which gets progressively worse and perhaps swelling close to the joint. Occasionally a dog will be presented to the veterinary practice with a broken limb and upon further investigation it will become clear that a bone tumour was the cause of the fracture, even if there was no previous evidence of disease.
A veterinary surgeon will need to perform some tests to diagnose this form of neoplasia correctly. Usually a dog which seems to be showing signs suggestive of osteosarcoma will be examined carefully by your vet who will pay particular attention to the limb itself, but also examine your pet generally to check for any obvious signs of metastasis (spread of the tumour). You will probably be offered radiography (X-rays) as the next stage of investigation; this will usually show the veterinary surgeon that there is a pathological condition in the limb. When X-rays are taken of the bones affected by osteosarcoma it is usually possible to see that a serious pathological condition is present in the bone. The appearance is much more aggressive than that of arthritis and it is usually fairly easy to distinguish between arthritic and neoplastic conditions in the bones. However if the radiographs are inconclusive your vet may offer to repeat them in a week or two to find out if the condition is progressing. It may also be necessary to take a biopsy sample of the bone for accurate diagnosis of osteosarcoma. This may allow a more accurate prognosis to be given as well. Radiographs may be taken to show any lesions in the lungs as osteosarcoma often spreads to these organs and presence of the tumour here dramatically reduces the chance of a good outcome following treatment of the patient. However thorough the examination of your pet, a vet can never be absolutely sure that metastasis has not occurred since tumour cells may be microscopic and not show up on X-ray or ultrasonography at the time of examination. I always assume that there is a strong likelihood that cancerous cells have already spread to other organs by the time I examine a pet with osteosarcoma for the first time due to the fact that it is such a rapidly progressing neoplasia. Other tests such as blood and urine samples may also be required, especially if your pet is going to undergo surgery for the condition. Occasionally more advanced diagnostic procedures may be necessary such as MRI or CT scans.
Osteosarcoma is a very difficult condition to treat and often the prognosis for pets suffering from this form of neoplasia is poor. It is an aggressive cancer which destroys the long bone itself causing pain, lameness and sometimes pathological fractures. It also spreads to other regions of the body readily (a process known as metastasis). It is carried to organs distant from the affected bone by the blood and lymph and often settles in the lungs or liver. Here it continues to damage the body and usually once metastasis has occurred the outlook for the pet is very poor. If a pathological fracture occurs in a bone due to osteosarcoma repair of the fracture will be impossible.
Often in cases of osteosarcoma involving one of the long bones in the leg, amputation of the affected limb will be advised. This often causes owners to worry and many are concerned about their pet's subsequent quality of life should they choose this option. I would strongly recommend that you consider very carefully the possibility of taking this option. Many people would rather have their pet euthanased than take this step but in reality most dogs do really well on three good legs and go on to have a good quality of life for the rest of their days. I have known very many dogs and cats who for one reason or another have undergone amputation of a limb, and in the vast majority of cases they are able to enjoy walks and play as much as before once they have recovered from the surgery. Remember that animals do not suffer from the psychological trauma which we humans would experience from the loss of a limb. They have an amazing ability to "bounce back" and get on with life which perhaps we people could learn from! If you are very opposed to the idea of an amputation then it is sometimes possible to remove the area of bone affected by the cancer and conserve the limb but this is a much more complicated procedure and possibly involves a longer recovery period for the pet.
Obviously there will be individual cases where amputation of the limb would not be in an animal's best interests, but if your pet is suitable do not rule it out unnecessarily. Cases in which amputation may be unsuitable include those animals which are unlikely to survive the surgery perhaps due to heart or kidney conditions, obese animals, pets with painful arthritic conditions in other limbs and of course those dogs in which the osteosarcoma has already spread and is affecting other organs of the body such as the lungs.
If surgical amputation is not an option for your pet there are other treatments which may palliate the condition, although of course the disease will progress and eventually be fatal. Analgesic drugs such as nonsteroidal anti-inflammatory drugs may be used to control the pain, exercise should obviously only be very gentle as eventually pathological fractures are likely to occur due to the cancer. Local radiation therapy may also be helpful in this condition. Chemotherapy may also be useful in the treatment of osteosarcoma following the amputation of the affected limb. Chemotherapy may be used to control the growth of metastatic cells present in other organs and may prolong the survival time of affected animals. The protocol for chemotherapy will be discussed with you by your veterinary surgeon if this is deemed to be suitable for your pet.
Since it is unknown why cancer develops in the bones it is impossible to know how to prevent it. Some authors believe that chronic low grade trauma may predispose to the development of osteosarcoma. Osteosarcoma has also been found in bones where metal implants have been used and this may also be a predisposing factor to the disease. If your dog is lame and this does not get better as expected then it may be wise to ask your vet to investigate the cause of the lameness in greater detail to hopefully rule out this very serious disease.