Bone Cancer in Large Breed Dogs

Bone tumours tend to affect the larger and giant breeds more than small dogs. Irish Wolfhounds, Great Danes, Rottweilers and German Shepherd dogs appear to be at particular risk.

The majority of bone tumours are of the type known as osteosarcoma - this is a malignant tumour arising from the bone cells themselves. Other tumours include fibrosarcoma (tumour arising from fibrous tissue), chondrosarcoma (cartilage origin), and haemangiosarcoma (blood vessel tumour).

A veterinarian can take radiographs (x-rays) to look for signs of abnormal bone growth that may indicate osteosarcoma. The characteristic sites for this abnormal growth are the leg bones, "away from the elbow, toward the knee." In the front leg the lesions would be in the radius (foreleg bone) toward the wrist, and in the humerus toward the armpit. In the hind limbs the lesions would be in the tibia (shin bone) and femur (thigh bone), close to the knee. Occasionally osteosarcoma is seen in the mandible, the lower jaw bone.

Osteosarcoma cannot be diagnosed with radiographs alone, since other types of cancers and other conditions can cause bone problems. Because proper treatment of cancer requires an accurate diagnosis, a veterinarian who suspects osteosarcoma after taking radiographs should refer a patient for a cytology and/or biopsy

To date, no familial or genetic factors have been identified although it has been postulated that the growth characteristics of the at-risk breeds are important. The tumours tend to arise in the limb bones with the most active growth plates i.e. distal radius, proximal humerus, distal femur, proximal tibia and distal tibia. The combination of the relatively rapid growth and the weight of the individual is implicated. Presentation.

Middle-aged dogs are more commonly affected and the first clinical sign that is noticed is either sudden onset lameness or a swelling at one of the characteristic sites. Bone tumours can be intensely painful, so much so that the dog can be severely affected by this and lameness, inappetence, 'grumpy' and generally poorly are common signs. As the tumour grows, the swelling and lameness increase and routine painkillers give little or no relief. Obviously not all sudden lameness and swellings are bone tumours - joint injuries such as sprains or ruptured ligaments can also cause the clinical signs. Veterinary attention should be sought at an early stage in all cases.

The prognosis for any bone tumour has to be grave. Without treatment, the primary tumour will become so painful that euthanasia will be the only option. Almost all bone tumours of the legs are malignant (cancerous) and therefore have the potential to spread. Most tumours of the bone will have spread long before the primary tumour is first noticed. Therefore, even when the primary tumour is cured the secondary tumours eventually grow to such a size that severe breathlessness and general malaise become over-whelming.

There is no simple treatment for bone tumours in dogs. It is a very serious disease and therefore requires aggressive therapy to achieve any chance of success. However in recent years, progress has been made:

1. Analgesics either with drugs or by radiotherapy to the primary site. The pain relief achieved by radiotherapy tends to be better and of longer duration than by drugs but even so the pain is likely to start up again within the next 6 -9 months. However, not all bone tumours are suitable for radiotherapy as destructive tumours are likely to fracture. Radiotherapy has no effect against the secondaries.

2. Limb salvage by removal of the affected bone and replacing this with a bony graft, a large metal plate and fusion of joint. This option is fraught with complications and even in the best hands there is a 30% - 40% failure rate.

3. Amputation is the only certain way of controlling the pain and primary tumour problem. Most dogs will cope very well with amputation including Rottweilers and Great Danes with the loss of a forelimb. The pain associated with the primary tumour is often so severe that the dog is walking on three legs, if they can manage at this stage they will be so much happier and pain-free without that leg.

4. Anti-cancer drugs can be used as an additional treatment with the last two options (ie: limb salvage and amputation) to control the rate at which secondaries develop. Following removal of the primary tumour by whatever means, but without use of drugs, 60% of dogs will develop secondaries (and have been put to sleep) by six months and only 1 in 10 survive to one year. With the use of chemotherapy (carboplatin-based infusion) the six months survival is about 60%, with 4 in 10 alive at one-year survival and about 20% alive at two years. Earlier diagnosis and more aggressive treatments may improve on this. Carboplatin treatment is not without its occasional problems; some nausea and vomiting may occur after the treatment but this usually resolves within a couple of days. Currently the drug is administered once every 3 weeks for four doses.

Bone tumours in dogs tend to affect the large and giant breeds. They are almost always malignant and secondary spread is a serious problem. Treatment is directed against the severe pain of the primary and amputation offers the best control - most large dogs can cope extremely well on three legs. Chemotherapy can slow down the rate at which secondaries grow and about 15 to 20% of dogs with osteosarcoma can now be cured. Further research and new drugs will help improve on this in the future. If you have any further questions about bone cancer or any other aspect of cancer in dogs you should speak to your veterinary surgeon who will be able to discuss this with you more fully.

If you are concerned about the health of your pet you should contact your veterinary surgeon.