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Canine Osteosarcoma Facts
What is Canine Osteosarcoma?
Canine osteosarcoma is the most common bone cancer in dogs. Dogs diagnosed with bone cancer 80%-85% of the time are diagnosed with canine osteosarcoma. Also called K9 OSA, K9 osteosarcoma, canine OSA and osteogenic sarcoma, the tumor is very aggressive. Treatment, whatever is chosen, should not be delayed.
Who gets Canine Osteosarcoma?
Any dog, at any age, can be diagnosed with K9 OSA, but usually develops around 7-9 years of age. Large or giant breed dogs, however, can be affected as early 1-2 years of age. Particularly prone to the disease are Saint Bernards, Rottweilers, Great Danes, Irish Setters, Doberman Pinschers, and Labrador Retrievers.
Male dogs seem to be more susceptible than females. But when both sexes are neutered, they become doubly at risk over dogs that are still intact.
Where is Canine Osteosarcoma Found?
K9 osteosarcomas are discovered approximately 75% of the time in the limbs (the appendicular skeleton). They generally attack the bones just above the wrist joint (distal radius), the bone of the upper arm close to the shoulder (proximal humerus), just above the knee on the lower part of the thigh bone (distal femur), or the upper part of the larger of the two leg bones right under the knee (proximal tibia).
While not as common tumors in the appendicular skeleton, osteogenic sarcomas can also be found in the axial skeleton: the cranium, spinal column, and ribs.
OSAs start deep inside the bone, literally exploding the bone as it grows outward. Becoming more and more painful, the highly aggressive tumor spreads to other areas of the body very rapidly, primarily invading through the blood, and, occasionally, through the lymph.
What are the Symptoms of K9 OSA in the Limbs?
The most common signals of appendicular canine OSA are: limping or lameness, inflammation, pain, and swelling. Pain results from micro, or pathologic, fractures. Swelling occurs from edema and fibrous tissue growth from a decrease in circulation. Or this can also mean the tumor has already infiltrated into the surrounding soft tissues.
Occasionally, a sudden fracture of the affected bone may be your first clue. Symptoms can seem to happen almost overnight.
What are the Symptoms of Canine Osteosarcoma in the Axial Skeleton? Dogs with axial osteosarcoma in the lower jaw bone (mandibular OSA) and bone tumors around the eye (orbital site tumors) will have problems swallowing. Dogs with cranial tumors or tumors in their vertebrae will have neurological problems. Dogs with pelvic osteosarcomas may have difficulty having a bowel movement.
What Causes Canine Osteosarcoma? Although canine osteosarcoma does not have a clearly defined cause, researchers have identified several factors that increase the likelihood of developing these tumors. Genetic predispositions in a dog’s family lineage, like aberrations of the p53 tumor suppressor gene, are thought to contribute. Former skeletal injuries, chronic bone infections, metal or bone implants or other foreign bodies join the list.
Factors, like puppy diets that cause rapid growth rates, may contribute to risk since dog bone cancers are often located near growth plates. And because osteosarcomas tend to be found in areas of increased bone remolding, oncologist Dr. Kim Cronin, at the University of Pennsylvania, feels that each time there is cell damage or increased turnover in an area, odds are the DNA will be more apt to make a mistake when coding for new cells, This can lead to tumor development.
Sodium fluoride in drinking water and the oral insect growth regulator diflubenzuron, commonly used for flea control, both carcinogens, may be factors.
Additionally, osteosarcomas have been induced in laboratory animals via DNA viruses (polyomavirus and SV-40 virus) as well as RNA viruses (type C retroviruses).
How is Canine Osteosarcoma Diagnosed?
To diagnose K9 OSA, your vet will take an X-ray of the suspected site. But besides a radiograph, diagnostics could entail a complete physical, orthopedic, and neurological workup to rule out other causes. If X-rays uncover an unquestionable bone tumor, most vets won’t suggest a biopsy at the time of diagnosis.
Still, if for some reason there is a question about the lesion on the X-rays, a very small section of bone may be biopsied.
Does Canine Osteosarcoma Spread (Metastasize) Quickly?
Yes, unfortunately, K9 OSA, is a very aggressive cancer that travels through the body very quickly. As soon as your dog is diagnosed, a chest X-ray may be taken to check for visible metastasis. At the time of diagnosis, osteosarcoma has already metastasized in 90% of the dogs.
The lungs are the most common place for the cancer to travel. But it is highly unlikely that spread will show up in the radiograph because metastases are small (less than 10% will initially show up on a chest x-ray). But since it has been found that 90% of the dogs diagnosed will already have metastasis, all dogs diagnosed with OSAs are treated as if they have lung metastasis no matter what the X-ray reveals.
If there are suspicious lymph nodes or skin masses, those cells may be biopsied. An abdominal ultrasound may be undertaken and possibly a bone scan may be used to evaluate how far the cancer has spread. But, because the disease moves so rapidly, many veterinarians may consider these steps academic.
What is the meaning of the word osteosarcoma? Osteo means “bone” and sarcoma comes from the Greek word sarx which means “flesh.” A sarcoma is a cancer that develops from the embryonic mesoderm and includes tumors of the bone, cartilage, fat, muscle, vascular and hematopoetic tissues.