Osteosarcoma in Dogs: Diagnosis, Treatment and Outcomes

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While Osteosarcoma represents just 5% of all canine tumors, it is estimated that between 6000 and 8000 new cases will be diagnosed this year in the United States. As the most common type of bone cancer in dogs, Osteosarcoma accounts for approximately 85% of canine tumors that originate in the skeletal system. This is an aggressive cancer where malignant tumors develop deep within the bone; from there they destroy healthy bone and remodel it with tumorous bone from the inside out.  The tumerous bone becomes increasingly painful and is not as strong as healthy bone, potentially causing the bone to break easily with minor injury.

Risk Factors Associated With Development of Osteosarcoma In Dogs

Osteosarcoma is generally a disease of large breed dogs, and although any size dog may develop the disease, it is estimated that large breeds such as the Scottish Deerhound are 200 times more likely to develop the disease than are toy breeds. High risk breeds include Rottweilers, Deerhounds, Greyhounds, Great Pyrenees and Mastiffs as well as other large breed dogs.  Typical age of onset is 7-10 years of age, however large breeds may develop the disease earlier, in fact there have been large breed cases with diagnosis as early as under one year of age.

Factors that are suspected in increasing risk of developing the disease in addition to breed size include puppy diets that promote rapid puppy growth, spay and neuter, genetics and environmental factors:

• As tumors are frequently found near growth plates, factors that affect the growth rate and promote rapid growth are suspected in increasing likelihood of developing this cancer. 
• One long term historical study of Rottweilers showed that the earlier that a puppy was spayed or neutered the more likely it was to develop Osteosarcoma. Casterated males are 65% more likely to develop this cancer than intact males, and spayed females are 35% more likely to develop the disease than intact females.
• As certain lines of dogs within breeds have an increased propensity for developing this cancer, a genetic component is suspected as well.
• Fluoridation of drinking water has been linked to the development of Osteosarcoma in studies of both rats and young men in the North Eastern United States.

Diagnosis of Oesteosarcoma

Symptoms of Osteosarcoma will vary based on the location of the primary tumor. As the tumor grows, the affected area becomes increasingly painful. Swelling eventually develops around the tumor and the area is painful to the touch. 

• Development of a tumor in a leg bone may cause sudden onset lameness or intermittent lameness over a period of several weeks.
• Dog with tumors in their jaw bones may exhibit difficulty swallowing and/or excessive drooling. 
• Dogs with cranial or spinal tumors may present with neurologic deficits. 
• Dogs with pelvic tumors may exhibit difficulty defecating as their primary symptom.

It is important to see a veterinarian as soon as you suspect the disease, as it progresses very rapidly.  In most instances once a diagnosis of Osteosarcoma has been made, it has already micrometastasized to other areas of the body including the lungs and other bones.  Additionally, as the tumorous bone is weaker than normal bone, it can fracture easily.  Pathological fractures resulting from Osteosarcoma will not heal, so it is important to begin treatment as soon as possible.

Diagnosis is initially made by x-ray.  Once a bone tumor is suspected, the veterinarian should take x-rays of the lungs as well to see if the tumor has metastasized to that area.  Prognosis and treatment options will vary greatly if metastasis is evident in the lungs.  The tumor will also be aspirated with a small needle to obtain a sample of the tumor for further analysis and determination of the nature of the tumor.  This procedure does carry a small risk that the aspiration of the tumor could fracture the already weakened bone.

Additionally, the vet may aspirate the lymph nodes or any skin masses, do a full blood panel and perform an abdominal ultrasound in order to determine the spread of the cancer and overall health of the dog.  A bone scan may be performed in order to determine the spread of the disease to other bones and the extent of the tumor in the primary location.

Treatment For Osteosarcoma

The standard of care for the treatment of Osteosarcoma requires that the tumor be removed to prevent further spread of the disease.  In most instances, this means amputation of the affected limb.  Dogs typically respond well to this treatment, however overweight dogs, arthritic dogs or elderly dogs may not be good candidates for amputation. 

If the tumor has not progressed too far, a limb sparing procedure may be attempted.  The most successful procedures are performed where the tumor is on the bone just above the wrist of the dog and the tumor is still relatively small in size. Generally in these procedures, the removed bone must be replaced with bone from another site on the dog or from a bone bank.  Since there is a high complication rate with this procedure and a longer, more involved recovery than an amputation, amputation may eventually be necessary anyway.

In cases where neither amputation nor limb sparing procedures can be performed, the dog may be treated with palliative radiation therapy.  While radiation will not extend the life of the dog, it can be an effective pain management tool to improve the quality of the remaining life of the dog. This treatment provides relief to approximately 75% of the dogs that receive this therapy.  Radiation doses are given 1 to 4 times and are usually administered at one week intervals.

Follow-up to surgical removal of the tumor or limb includes chemotherapy.  In most instances the tumor has already micrometastisized at the time of diagnosis.  Chemotherapy, while not effective in treating tumors with visible signs of existence, is effective at destroying the microscopic disease.

Updated 11/5/13: Breakthrough in Pain Management for Dogs Suffering with Osteosarcoma

Prognosis After Treatment For Osteosarcoma

Following surgery, dogs that do not receive chemotherapy can expect an average life span of an additional 3 months post surgery.  Those treated with chemotherapy may enjoy a median lifespan of one year.  Approximately 50% treated with both surgery and chemotherapy will survive 1 year, less than 30% will survive two years and 10% will make it to 3 years.  While these statistics sound discouraging, it is important to keep in mind that in dog years, and especially in large breeds with shorter life expectancies, an additional year represents between 10-13% of a dog’s total expected life span.

Improving Your Dogs Odds In Preventing Development Of Osteosarcoma

If you have a large breed dog, or are aware that this issue has developed within your dog’s lines, there are some precautions you can take to improve his odds at heading-off or delaying the onset of the disease.

• Feed your puppy an “all life stages” dog food, and not a specially formulated puppy food that will accelerate growth.
• Wait until your dog is at least one year old before spaying or neutering him or her.  Leave males intact if you have a well fenced yard and no intact females in the home.
• Provide spring water for drinking water for your dog; carbon based filters such as PUR and Brita do not remove fluoride.
• Regularly examine your dog while petting for lumps and sensitive areas as he ages.