Bone cancer is a highly malignant cancer and most common in older large- and giant-breed dogs. The causes for bone cancer are not yet well understood, but it is fairly easy to diagnose. Symptoms of bone cancer are pain, swelling and sometimes bone breakage. Clinical signs are usually easy to see on X-rays.
Most dogs who develop bone cancer are middle-aged and older, although it can sometimes strike young dogs. It affects almost exclusively large and giant breeds. Rottweilers, Greyhounds, Bernese Mountain Dogs, Wolfhounds, Great Danes and Newfoundlands are some of the commonly affected breeds.
Bone cancer often develops at the site of an earlier injury or surgery. Dogs who have had orthopaedic surgery for dysplasia, anterior cruciate ligament repair and similar surgeries are more at risk.
There is some speculation that factors such as early neutering, over-vaccinating and poor diet may contribute to bone cancer.
By far the most common type of bone cancer in dogs is osteosarcoma (OSA), accounting for about 85 per cent of all cases of bone cancer. OSA tumours usually develop in the long bones of the legs, although they can occur in the spine, skull and jaw.
Other types of bone cancers include synovial cell sarcoma, hemangiosarcoma, chondrosarcoma and fibrosarcoma. Synovial cell sarcoma and chrondosarcoma originate in the connective tissues around the joints and invade the bone. The other types may appear on virtually any part of the dog's skeleton.
Over all, most bone cancer tumours usually grow in the dog's leg bones. Some tumours are very slow growing, starting deep in the bone, while others are aggressive and grow quickly. Most often the first symptom is a slight limp which grows progressively worse as the tumour destroys the bone. Depending on the location and type of cancer, there may or may not be a lump or swelling. Some stoic dogs with fast growing tumours will not show signs of pain, like limping, and will be normally active until a fall or slip causes the weakened bone to snap.
Tumours in the spine and ribcage may cause limping and general stiffness. Bone cancer in the dog's skull or jaw usually affect chewing and eating. Swelling and lumps are more common in skull and jaw cancer. In rare cases, the tumour may affect brain functioning, causing aberrant behaviour and personality changes.
While dogs with cancer may be asymptomatic at first, excruciating pain is a hallmark of all bone cancer. In later stages even strong opiates and pain medication do not mask the pain.
OSA has a characteristic "swiss cheese" appearance when viewed in X-rays because the bone is literally being eaten away. Other bone cancers may appear cloudy, or a cancerous mass can easily be seen. Because OSA is highly likely to metastasise, some veterinarians will do an ultrasound of the organs to see the extent of the spread. OSA most often spreads first to the lungs, where it is visible as small dark spots.
Some veterinarians will suggest a bone biopsy, but oncologists and experts generally agree that adds unecessary pain to the dog and costs to the owner. If the diagnosis is unclear, imaging with more sophisticated equipment is recommended instead.
Bone cancer treatment primarily depends on the type and location of the cancer and the financial situation of the owner. Chemotherapy and cancer treatment can be extremely expensive. Owners may opt for managing the pain as long as possible, or for limb amputation to remove the source of the pain. Other options include radiation, bone-sparing surgery, chemotherapy and complementary medicine.
Sadly, euthanasia is often recommended for dogs with advanced bone cancer, particularly if the owners do not have the financial means for expensive surgeries or treatments.