WASHINGTON (CIRCA) — Osteosarcoma (OSA) is one of the most common forms of bone cancer seen in veterinary patients. Most often, this devastating disease is seen in large-breed, intact (not spayed/neutered) dogs, although any dog or cat is susceptible.
The disease most commonly affects the appendicular skeleton, so the limbs are the most likely area of the body to be impacted. We also use the slogan "toward the knee and away from the elbow" to refer to where on the limbs this disease is most likely to appear.
This case involves a male, intact German shepherd dog who was presented to the clinic for pain in his shoulder. All veterinary visits start with history and a physical exam (PE). Unfortunately, Rex was an aggressive dog who was also in a lot of pain, which made performing a full PE impossible without sedation. So, Rex was given pain medication and returned for sedation and radiographs (X-rays) of the affected left front limb.
On the images, it was immediately clear that there was a lytic, destructive bone lesion at the proximal end of Rex's humerus (end of the bone closet to Rex's body). Remember, OSA most commonly occurs toward the knee and away from the elbow, so proximal humerus makes sense.
Typically, in these cases, the affected limb is amputated, which provides the patient immediate relief from pain. We also check for metastasis (spread of disease to other parts of the body) and pursue chemotherapy options whenever possible.
Unfortunately, it is estimated that about 90 percent of animals have metastasis at the time of initial diagnosis, even if the metastasis is microscopic and thus not readily discernible on imaging modalities available to use (CT scans, MRIs, ultrasounds and radiographs). Of those animals treated aggressively (surgery and chemotherapy), 50 percent will be alive 12 months following diagnosis. Animals treated less aggressively have, on average, a six-month survival time.
This is one of my least favorite diseases to treat, because of the prognosis and because of my own experience with my family's Rottweiler when I was growing up.
As such, I always encourage owners to value every moment with their pet (as always) but particularly when faced with such an upsetting diagnosis.
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