Canine osteosarcoma is commonly known as bone cancer in dogs. Since losing a dog to OSA in the past year, I have become more aware of its high incidence in the Irish Setter. Hardly a month goes by without learning of another affected Irishman and his owner's heartbreak over the thought of losing a beloved companion.
And since my dog, Cruiser, was diagnosed in September 1999, I have learned a lot about the disease and of the many treatment options now available to help fight OSA and offer good quality of life.
Facts and Figures
OSA is the most common primary (meaning original site or non-metastatic site) bone tumor in dogs. It is estimated to occur in 8 - 10,000 dogs (any breed) per year in the U.S. alone. Large and giant breeds are more at risk. Taller individuals within a breed have an increased chance of developing OSA. The theory here is that the development of OSA is related to rapid bone growth - either in abnormal cell metabolism associated with rapid bone growth in young large breed dogs or strenuous activity (just think of a typical young Irish playing!) causing micro-fractures during periods of rapid growth and the micro-fractures then induce osteosarcoma formation later. The larger breeds have longer growth periods and are subject to rapid growth spurts thus leading to the above. There is also an increased incidence with age. (In the 1997 ISCA Health study, 75% of affected Irish Setters were between the ages of 8 and 13 years.) Sex of the individual is of unknown influence, and varies with each breed and tumor location.
Other theories related to the cause of OSA include an inheritance of genes unrelated to size but predisposing to OSA. There is speculation on a genetic cause involving genes that normally act as tumor suppressor genes, which are altered thus preventing normal action.
Having had previous soft tissue radiation also increases the risk of OSA. As does having a metallic implant (fracture repair). This is very rare though and should not discourage an owner from repairing a fracture.
OSA is locally destructive to normal bone tissue and can cause the bone to be weakened to the point of spontaneously fracturing (pathological fracture). It is very painful in the active stage. OSA affects the appendicular skeleton (legs) 75% of the time; the front legs are affected twice as often as the hind. The most common site is the small region between the shaft and the ends of the long bones - the metaphysis, where growth occurs. The most common bone affected is the radius (distal end).
OSA is very aggressive and has a high metastatic rate - usually to the lung. Undetectable mets are present 80 - 90% of the time of diagnosis. If there is no treatment, the dog usually succumbs within 1 to 2 months of diagnosis.
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