Osteosarcoma in Dogs

Osteosarcoma is the most common bone tumor in dogs, particularly affecting the leg bones of large breeds such as the Great Dane and Irish Wolfhound. However, it can affect any dog of any breed, and appear in any bone structure. Osteosarcoma is one of the more serious cancers a dog can have, as it spreads quickly and is difficult to remove surgically. The tumor initially appears as a swollen or painful area on a dog’s leg, causing a limp or whining and licking. This cancerous bone is significantly weaker than healthy bone, and may break unexpectedly. See a veterinarian immediately if you detect any abnormalities on your dog’s legs or body.

• Painful, swollen lump on long bones
• Unusual nodular feeling beneath skin
• Limping or appearing weak
• Sudden breakage of bone from moderate physical activity

• Lifetime accumulated exposure to carcinogens
• Genetic predisposition

If an owner notices a swollen, hard area on their dog’s leg unrelated to a past injury or a recent trauma, they schedule a visit with the veterinarian right away. A veterinarian will want to x-ray the affected body part to determine what is wrong. Osteosarcoma has a number of key attributes that are easily identifiable on a radiograph. A lytic lesion is an area of eroded bone caused by the sarcoma. A sunburst pattern indicates rapid tumor growth as the normal bone is forced outward. Fractures may be found through the abnormal bone, as it is weaker and grows faster.

If the veterinarian sees any of these features on the bone, they will want to perform a biopsy, in which a small sample of the affected bone is sent to the lab for testing. Lab analysis is the only way to be completely sure of an osteosarcoma diagnosis. The veterinarian will also perform an alkaline phosphatase assay as part of a basic blood panel. High alkaline phosphates is associated with a poor outlook and will affect decisions about chemotherapy.

Osteosarcoma is a very aggressive cancer, and by the time it is detected, usually has metastasized (gained the ability to spread body-wide). An assessment of the current state of the cancer will determine the treatment method. If the cancer has been caught early, and there are no tumors in the lymph nodes or lungs, chemotherapy may be considered an option. However, the rate of survival at 2 years for dogs treated with the most effective chemotherapeutic, Cisplatin, is still between 7 and 21%. For Cisplatin to be effective at prolonging your dog’s life, the whole course of treatment must be taken. Giving less than 3 doses has not been found to extend survival time. Given the expense of the treatment and the severity of the cancer, palliative treatment is the usual course of action for dogs with osteosarcoma.

Often, the pain of osteosarcoma is so great that the affected limb must be amputated. This removes the tumor and in nearly all cases resolves the pain. Dogs quickly learn to run and lead a normal life after the amputation. However, there are a number of limb-sparing surgeries that are possible based on the extent of the tumor and the age of the dog. The benefits of these surgeries come with the cost of reduced mobility in the limb, increased ease of fracture, and incomplete reduction of the pain.

Unfortunately, the outlook for osteosarcoma is fatal in nearly all patients. Analgesics (painkillers) can be administered to manage pain. There are a wide variety of these available, with different effects and drawbacks. Non-steroidal anti-inflammatory drugs have a mid-level pain control ability, but also lessen pain by reducing inflammation. These drugs are processed through the liver and kidneys, and thus excessive doses should not be given, and a different therapy found for patients with pre-existing liver and kidney ailments.

Narcotic pain relievers are effective in managing severe pain but have the side effect of causing drowsiness, disorientation and nausea. If your pet is sufficient pain to receive these types of medication, a veterinarian may recommend the dog be put down when moderate doses are no longer enough.