Osteosarcoma continues to be one of the most challenging types of cancer to treat. Part of the therapeutic challenge arises from the fact that at the time of diagnosis there often has already been metastasis to other areas of the body.
|This image is of a pathological fracture of the femur that was caused by cancer of the bone weakening the bone structure||This closer side view of the pathological fracture is of the patient on the left||The arrow points to bone cancer invading the lateral side of the humerus near the elbow joint||This image displays extreme dissolution of the distal two thirds of the ulna of a dog due to bone cancer|
"Unfortunately, at the first signs of lameness," says Dr. Kenneth M. Rassnick, Assistant Professor of Oncology at Cornell University College of Veterinary Medicine, "we expect that the tumor has already metastasized. However, as long as the metastatic cells are still microscopic and we cannot detect them on radiographs, then dogs will still benefit from treatment."
There is no single treatment protocol for all patients with bone cancer; Rassnick explains that individualized strategies are selected for each patient. "Currently, for dogs with osteosarcoma, I thoroughly screen them for obvious signs of metastasis. For most dogs, this includes radiographs of the lungs and physical examination and palpation of other bones. Amputation of the affected leg is the first line of treatment but unfortunately, amputation alone is only palliative for a cancer as aggressive as osteosarcoma. Over time, the metastatic cells will continue to grow in number and size. If it is determined by radiography, ultrasound or physical exam that there are no metastatic tumors present, amputation of the affected leg followed by chemotherapy has proved to be the most effective treatment for osteosarcoma. There are a number of chemotherapy regimens that we know to be effective at controlling the metastatic cells."
Thoughtful consultation with the veterinarian regarding chemotherapy is very important. Rassnick tells us "The exact chemotherapy protocol will depend on a number of factors including overall health status of the dog and function of organs such as the heart and kidneys. We have spent a considerable amount of time trying to determine the best time to begin chemotherapy. Since we know the cancer cells have already spread, it is tempting to begin therapy as soon as possible. Some have even advocated giving chemotherapy before the amputation surgery or even at the same time. Our studies have shown there is not a tremendous benefit to instituting therapy that soon, so I generally recommend having the amputation surgery done, letting my patients heal for 7-14 days and then begin chemotherapy when the stitches are ready to be removed."
Not all dogs will be candidates for amputation. Rassnick adds "Some dogs may have concurrent orthopedic or neurologic problems that may complicate ambulating with three legs, or occasionally it is the wish of the family not to pursue the surgery. We can offer palliative options for controlling bone pain including nonsteroidal medications and even radiation therapy. Localized radiation therapy to the diseased bone is often a very effective method at controlling the pain and some veterinary oncologists can now offer this as an option."
As drastic as amputation seems to be, it should not be immediately rejected as an attempt at treatment. As a practitioner for over thirty years I have been amazed at how some canine amputee patients respond and adapt. Each case should be evaluated on its own merits with attention paid to such factors as the presence of arthritis in the patient, degree of excess body weight, heart and other organ function, and the patient’s attitude and ability to adapt to new situations.
Until new research reveals more about the menace of cancer’s mysterious origins and until ways are found to turn off rapidly multiplying cancer cells, we will need to be on the alert for bone cancer in our dogs. A veterinarian should evaluate any lameness that persists longer than three days. All dog owners should be proactive in requesting that an x-ray evaluation be done especially if swelling is present. And no matter what the diagnosis for the lameness is, be certain to let your veterinarian know if the expected healing and return to normal function has not occurred within the expected time frame.
The sooner bone cancer is discovered, the better the chances that treatment will actually affect a cure.
Image: Priority Pet Hospital / via Flickr