WHAT IS CANINE OSTEOSARCOMA?
Osteosarcoma is the most common type of bone cancer in dogs. It can occur anywhere on the skeleton, however it is most commonly diagnosed at the end of the bones (metaphysis) of the legs. This cancer has many similarities to osteosarcoma in children. It is painful in both kids and dogs. It almost always metastasizes (spread) to other organs, especially the lungs and other bones. It is said that up to 85% of tumors originating in the skeletal system is osteosarcoma. Osteosarcoma as a rule becomes evident in the later years when a dog is between the ages of 7 to ten.
THE CAUSES OF CANINE OSTEOSARCOMA
Canine osteosarcoma occurs most commonly in large or giant breeds, such as Great Danes, Scottish Deerhounds, Rottweilers, and Greyhounds. The risk also seems to increase when young dogs are fed diets that promote rapid growth.
SYMPTOMS OF CANINE OSTEOSARCOMA
Most dogs with osteosarcoma have a history of acute lameness or pain. Since osteosarcoma is frequently found in the bones that may be around or involving the shoulder, knee, and wrist, the first visible symptom is lameness in the affected leg. There might also be some swelling, inflammation, and/or tenderness near the region of the tumor. The dog might also be lethargic and not want to eat. Sometimes the dog will have a growth on their body as well. Other symptoms that might be observed are:
Pain (often severe)
Broken bones at the tumor site (called “pathologic fractures”); caused by bone weakness from the cancer; usually no history of physical injury to the area
Swollen upper jaw (maxilla); usually painful
Swollen lower jaw (mandible); usually painful
Pain when opening the mouth
Swelling and pain along the spine
Swelling and pain around the ribs
Difficulty eating or chewing (dysphagia)
Respiratory distress (difficulty breathing; dyspnea); typically caused by rapid spread [metastasis] of the cancer from bone to lung tissue; can also be caused by osteosarcoma of the ribs)
DETECTION AND STAGING
If the symptoms presented to the veterinarian are lameness, pain, and/or swelling and other issues have been ruled out. Frequently osteosarcoma has a characteristic appearance noted when X-ray images are acquired. Lesions are often detected along the bone, both destructive and productive.
The process of determining the extent of the disease is called staging. Staging is completed with a series of diagnostic tests, to try to determine where else the cancer might have spread. Minimally this will normally include some routine blood work, urinalysis, three-view chest x-rays or CT scan (to look for metastatic disease), and palpation and evaluation of other bones in the body. An abdominal ultrasound may be of help to the veterinarian to determine the course of action, as is a biopsy and/or needle aspirate, which is then sent to a pathologist. This will establish the type of tumor present.
Finally, a simple test to determine whether or not the tumor has spread to other bones might be suggested. This is called a bone scan, and might require an overnight hospital stay.
Two challenges exist when caring for a pet with osteosarcoma. The first is how to treat the bone tumor itself. The second is how to delay or prevent recurrence or spread of the tumor. Regardless of the treatments chosen, every attempt must be made to ensure that the patient is comfortable with analgesics (e.g., Piroxicam, tramadol, gabapentin, etc.) without any nausea or diarrhea. Finally, it is very important to ensure that nutritional support be addressed by ensuring a diet that is relatively low in simple carbohydrates with moderate levels of high quality proteins, relatively low amounts of red meat fats and relatively high levels of fatty acids from fish or algae sources that contain docosahexaenoic acid.
If there is no evidence that the osteosarcoma has spread, the most common recommendation is surgery to remove the lesion, or to treat the tumor with radiation. If surgery is selected, then removal of the limb is the quickest, least expensive, most effective way of alleviating pain and removing the cancer. The surgery is not a complicated one, and dogs are usually up and around very quickly – and don’t forget that dogs do very well with only three legs! Another surgery that might be considered is called limb sparing surgery. In this procedure, the tumor is removed without removing the limb.
An alternative to removal of the limb via amputation or limb sparing surgery is palliative or definitive radiation therapy. Palliative radiation is given in a few (2-5) dosages to first provide comfort, second to slow the rate of progression of the tumor, and third to occasionally reduce the size of the mass. Definitive radiation therapy is done to have longer term control of the tumor by administering smaller doses of radiation more frequently, or stereotactic radiosurgery (SRS). SRS allows a higher dose of radiation to be delivered to the tumor with a low chance of damage to the surrounding tissue. SRS is only available in some select cancer centers.
Once the tumor itself is addressed with surgery or radiation, then recommendations are often given to delay or prevent recurrence and spread of the tumor. There are other drugs that can also be given in the case of a dog who is not tolerating the chemotherapy very well due to nausea and other issues, but most dogs do well without that type of intervention.
The most important thing to remember when treating this type of canine cancer is the dogs’ quality of life. When appropriate treatment is employed, the average dog will survive from 10-14 months, and be able to enjoy a good to excellent quality of life for most of that time.