Dog Bone Cancer
Dog Bone Cancer:
What is it?
Dog bone cancer for most dogs describes canine osteosarcoma (K9 OSA) since it accounts for 80%-85% of all dog bone cancers. Canine OSAs can occur at any age, but primarily occur between 7-9 years of age, developing as young as 1-2 years of age in the larger breeds.
Large or giant breed dogs, including Saint Bernards, Great Danes, Rottweilers, Golden Retrievers, Irish Setters, Labrador Retrievers, and Doberman Pinschers, are particularly susceptible.
While males are more commonly affected than females, when neutered, both sexes become twice as susceptible compared to those who are intact.
K9 osteosarcomas are found about 75% of the time in the limbs. Known as the appendicular skeleton, K9 OSAs usually strike the bones above the wrist joint (distal radius), the upper arm bone near the shoulder (proximal humerus), the lower part of the thigh bone just above the knee (distal femur), or the upper part of the larger of the two leg bones just below the knee (proximal tibia).
OSAs can also affect the axial skeleton, i.e., the cranium, spinal column, and ribs.
Osteosarcoma develops deep within the bone, becoming progressively more painful as it grows outward. Exploding the bone from the inside out, the highly invasive tumor spreads to other areas of the body very rapidly, primarily traveling through the blood, and, rarely, through the lymph.
And while extra-skeletal OSA is rare, primary tumors have been found in the adrenal gland, eye, kidney, intestine, liver, mammary gland, mesentery, skin, spleen, testicle, and vagina.
Dog Bone Cancer Symptoms
Nikki, my large Standard Poodle, was diagnosed with distal radius OSA at 8.5 years of age. When we went to the vet, his wrist was swollen and he was limping. His clip included cuffs, so I had no idea if the swelling was progressive or if the cancer just presented itself all-of-a-sudden. I do recall him, a few weeks earlier, rounding a corner at break-neck speed and seeing him catch himself as his feet seemed to slip out from under him. I had never seen that happen before. But he appeared fine afterward.
The most common indications of appendicular OSA are: lameness due to micro, or pathologic, fractures and/or inflammation, pain, and swelling. Swelling is primarily the result of edema and fibrous tissue growth caused by decreased circulation. It can also indicate the tumor has extended into the surrounding soft tissues. Symptoms can develop very quickly. Occasionally, a sudden fracture of the effected bone may be a primary indicator.
The most common symptom of dogs with axial OSA in the lower jaw bone (mandibular OSA) and tumors in bone around the eye (orbital site tumors) is difficulty swallowing. Dogs with skull tumors (cranial OSA) or tumors in their vertebrae (vertebral tumors) will display neurological problems. Those with pelvic masses may have difficulty having a bowel movement.
Dog Bone Cancer Causes
The exact cause of canine osteosarcoma isn’t known. That being said, there is an alternative school of thought that believes all cancers are caused by a lack of pancreatic enzymes and that cancer is a symptom of this inadequacy, much like diabetes is a lack of insulin. The evidence is compelling. (see Enzyme Therapy under “Categories”)
Contributing factors may include genetic predisposition in certain family lines, such as: aberrations of the p53 tumor suppressor gene. Chemical carcinogens, including sodium fluoride in drinking water and diflubenzuron, a popular insect growth regulator used orally for flea control in dogs and cats, may be involved. Pre-existing skeletal abnormalities, such as: a former injury or chronic bone infection, foreign bodies (a metal, or bone, implant) have been cited. Additionally, DNA viruses (polyomavirus and SV-40 virus) as well as RNA viruses (type C retroviruses) have been found to induce OSA in laboratory animals.
Because osteosarcomas are often located near growth plates, factors affecting growth rates, such as diets that promote rapid growth in puppies, may predispose risk. Since OSAs tend to fix themselves in regions of increased bone remolding, Dr. Kim Cronin, oncologist at the University of Pennsylvania, has stated, “Every time you have cell damage or increased turnover, the DNA is more likely to make a mistake when coding for new cells, which can lead to tumor formation.”
Canine Osteosarcoma Diagnosis
Nikki’s diagnosis was a simple radiograph (X-ray) of his left wrist. Dr. Sam could see the star-burst pattern and bone lysis.
But besides a regional X-ray, diagnostics could include complete physical, orthopedic, and neurological exams to rule out other causes of lameness. If the radiograph(s) reveal a definite bone tumor, most vets won’t feel a biopsy is needed.
However, if results are not clear and a question exists about the lesion on the X-rays, a tiny section of bone may be taken for a biopsy to identify the type of tumor you are dealing with.
Canine Osteosarcoma Metastasis
If you are dealing with OSA, a chest X-ray may be taken to check for visible metastasis. In 90% of the cases, the osteosarcoma has already metastasized by the time it is diagnosed. Lungs are the most common site for metastases. Because metastases are small (less than 10% will initially show up on a chest x-ray) and since 90% of the dogs diagnosed already have metastasis, all dogs diagnosed with osteosarcomas are treated as if they have lung metastasis whatever the radiograph reveals.
If lymph nodes or skin masses are suspect, the specific cells may be sampled. An abdominal ultrasound may be done, possibly a bone scan to assess the spread of the cancer. However, many veterinarians may consider these steps academic, since the disease moves so rapidly.
See Treatment Options.