Brick, two days after amputation.

Here’s another topic from my personal file: On Monday of this week, our dog Brick was diagnosed with a bone tumor in his right knee. On Tuesday, the leg was amputated. Even before he has a chance to adjust to being one leg short of a full set, we are making our appointments with the oncologist and the physical therapist. This whirlwind has reminded me of how sudden the diagnosis of bone tumors can be and how quickly the owners and their veterinarians must respond.

There are four main types of malignancy that arise as primary tumors in bones: osteosarcoma, chondrosarcoma, fibrosarcoma, and hemangiosarcoma. Behaviorally, these tumors are distinct from the other tumor types, such as the carcinomas, that are known to send their distant metastases to bone. Of the primary bone tumors, osteosarcoma is by far the most common. It appears most frequently in the legs of large-to-giant breed dogs, but can sometimes present in the vertebrae, ribs, or pelvis of smaller dogs. Our dog, Brick, is a 100-lb mixed breed dog whose stature puts him somewhere close to “giant,” making this a textbook presentation of an osteosarcoma.

Clinical signs: The two things an owner first notices when a dog develops osteosarcoma: severe pain (often the dog stops using the affected limb) and a firm mass attached to a bone. This combination warrants immediate veterinary attention.

Diagnosis: A tentative diagnosis is made through a physical exam and radiographs. A final diagnosis, however, requires a bone biopsy, which can be tricky in a bone that is becoming increasingly fragile due to the tumor that is destroying it. Knowing that close to 80% of primary bone tumors are osteosarcoma, the veterinarian will usually offer the following work up: blood work followed by chest radiographs and abdominal ultrasound to rule out any visible metastases. Some veterinarians might also offer a “bone scan” or scintigraphy to look for bone metastases. If bone, lung, or abdominal metastases are evident, the next steps might involve surgery, chemotherapy, radiation therapy, or simply pain control.

Surgical Treatment: Barring any surprises on the lab work and imaging, the next step typically is surgery to remove the tumor. This can be a complete amputation or a “limb sparing” procedure in which only the tumor is removed and a bone graft is put in its place. The condition of the limb and the dog help to dictate which surgery should be considered. The tumor goes to the pathologist, who will confirm the diagnosis and provide the oncologist with information useful in planning treatment. For some dogs, the treatment will stop here. These dogs have a life expectancy of 4-5 months, on average.

Chemotherapeutic Treatment: The purpose of chemotherapy is to catch the metastases that spread before the primary tumor was removed; a whopping 90% of osteosarcomas have metastasized before they are discovered. There are a few different protocols developed for osteosarcoma, typically relying on some combination of cisplatin, carboplatin, and doxorubicin. Each of these drugs has a set of potential adverse effects and the protocol must be tailored to the health and the needs of each canine patient. Those dogs that undergo chemotherapy have an average of 12 to 18 months added to their lives.

There are some helpful resources out there to educate and support owners whose dogs are diagnosed with a bone tumor. One I personally find useful is I think I’ll be spending some quality time there over the coming months.

[note: there is a follow-up to this post, dated January 15, 2011]