What is osteosarcoma? Osteosarcoma is the most common bone tumour in dogs. It is much rarer in cats. It is a malignant type of tumour and can therefore infiltrate into the surrounding tissues, recur if removed and spread to distant tissues with the blood stream, for instance to the lungs or to other bones. What dogs are affected?
This tumour is particularly common in the large and giant breeds of dog and affects dogs of all ages, but those between the age of four and twelve are most commonly affected. There are certain predilection sites, which means that the tumour is most likely to arise in those spots. These are the long bones of the front and hind leg, for instance the lower front leg, just above the carpus, or wrist joint. However, osteosarcomas are also seen in other bones, such as ribs, skull bones, vertebrae or pelvis. Symptoms of osteosarcoma are dependent on the bone or bones involved, but in general it leads to a hard and very painful swelling, lameness and in cases where the tumour is not growing fast, muscle wastage. X-rays will give further information about the changes in the bones, but for a definite diagnosis it is often necessary to do a biopsy. This is the removal of a small part of the swelling, which can then be examined under the microscope in the laboratory to get a definite diagnosis. This histology test, as it is called, may take some time, as the bone has to be demineralised first before it can be cut into the very thin slices necessary for the investigation. Treatment of osteosarcoma is not always possible. If one of the long bones in the legs is affected, it is often necessary to amputate the entire leg. In rare cases it may be possible to do a salvage procedure, in which other bones are used to replace the tumorous bone, for instance a rib. In all cases it is necessary to establish first, whether there are any metastases. These are distant spreadings of the tumour. To this purpose, your vet will nearly certainly take x-rays of the lungs, as these organs are often the first to be affected. If there are already metastases, it is not generally advised to treat the dog. Chemotherapy is also used in the treatment of osteosarcoma. The drugs used for this are quite expensive and need to be used with extreme care. Dogs undergoing chemotherapy will need to have many blood tests taken during the treatment, but do normally not suffer any of the side effects which are often seen in humans, such as sickness or hair loss. Even though dogs with osteosarcoma can be treated, most dogs will die within six to twelve months due to metastatic disease. This is because the disease has nearly always already spread at the time of diagnosis, even though at this stage this may not be visible on x-rays. Therefore the prognosis for a dog with osteosarcoma is extremely poor.