Dog And Cat Osteosarcoma
It’s an ugly word for an ugly disease.
And it’s taking my friend, Catherine, pictured below, whom I’ve been treating since 2003.
Let’s break down the word. “Osteo” is a Latin prefix referring to bone. “Sarcoma” describes a group of usually malignant tumors of connective tissue such as bone, ligament, fat, cartilage and various fibrous tissues of the body.
Osteosarcoma in dogs typically affects large breed dogs more often than small breeds and female dogs and cats more often than males.
It even has its own saying, “Away from the elbow, toward the knee.” Thus, the most common sites are the middle of the humerus (upper arm), the radius (forearm) near the carpus (wrist), the end of the femur (thighbone) as well as the upper part of the tibia (shinbone). Any bone in the body can be affected. I once diagnosed a patient with osteosarcoma of a rib. The mandible (jawbone) is another common site.
Most pet owners have no thought of cancer when their animals are first diagnosed with osteosarcoma. The most common presenting complaint is limping. Many pets are in extreme pain and may cry out when the affected area is touched.
If owners see or feel a growth or swelling on the limb the condition is already very advanced. Such victims may suffer pathologic fractures which are broken bones caused by weakness the cancer has caused.
Sometimes a very fortunate dog or cat will have osteosarcoma diagnosed so early that there are no signs. I once found a little swollen area in the radius of a favorite patient, Maddie:. Even the very attentive owners had not yet felt it. Maddie had come to see us for a routine vaccination visit that turned out to be anything but routine.
Patients with an extremely early diagnosis have the very best prognosis because they may have little or no spread of cancer from the primary site to other locations.
Spread is the key word in dealing with osteosarcoma prognosis. Some oncologists believe that any osteosarcoma big enough to be diagnosed has already spread. They base this assumption on the fact that blood circulation through the bone marrow quickly spreads cancer cells, and they probably are right. Most oncologists agree that treatment of osteosarcoma is only buying time. Cure happens in very few cases.
Cures do occur, however. Maddie is an example. The day after we obtained her suspicious X-rays we overnighted them to a radiologist for a confirmation of our diagnosis. This was before digital radiography and the ability to e-mail images instantly via the Internet.
Maddie’s chest X-ray was clear, there was no evidence of cancer spread.
Within two days we had amputated Maddie’s left front leg. Amputation is considered first-line defense against metastasis (spread of cancer). (For a MyPetsDoctor.com story on amputation success stories click here.) We overnighted Maddie’s amputated leg to a pathologist for a histologic (microscopic, cell-based) diagnosis and, as soon as we had the pathologist’s confirmation we began aggressive chemotherapy.
If Maddie had metastatic osteosarcoma the chemotherapy took care of it, because she lived another five years after the diagnosis, and never suffered recurrence of cancer, dying instead of an unrelated condition.
If this were a commercial we would insert here “Results are not typical.” As I said in the beginning, therapy for osteosarcoma is mainly aimed at buying time, and most patients do die of it, eventually, regardless of the aggressiveness of treatment.
Still, not every diagnosis of osteosarcoma is an instant death sentence. Like Maddie, your pet may be relatively young when diagnosed. If you are thinking of proceeding with treatment, here are some factors to consider:
- Chest X-ray: the lungs act as a filter for cancer cells, and circulating abnormal cells often lodge there and begin to multiply until they grow into a full-fledged mass, visible on radiographs. Most oncologists agree that if there is spread to the lungs there is also spread to many other parts of the body and treatment should be limited to pain control and palliative therapy.
- Body weight: if your pet’s weight is normal to slightly thin he has the best prognosis for healing from amputation or limb-sparing surgery. If your dog’s weight is too great to carry on three legs, he may not be a candidate for amputation.
- Pre-existing orthopaedic conditions: Crippling arthritis in one or more legs may prevent your dog from functioning after amputation, even with a normal body weight. Previous amputation is also a pre-existing orthopaedic condition. I was once at an orthopaedic conference during which the speaker showed a photograph of a dog who could walk on two diagonally-opposite legs, having had one leg amputated after trauma, then losing a second leg to osteosarcoma.
- Amputation vs. limb-sparing surgery: Until a decade or so ago amputation was the first therapeutic step for dog and cat osteosarcoma patients. Later, surgeons developed procedures that allowed removal of the diseased portion of the bone, followed by the insertion of bone grafts so that bone cancer victims could keep their legs. That’s the up side. The down side is that sometimes cancerous bone is left behind. Also, the procedures are very invasive and very expensive. As orthopedic procedures go, amputation is fairly inexpensive.
- Chemotherapy: for dog and cat bone cancer, chemotherapy is given intravenously, so nearly every tissue in the body is bathed in cancer-killing medication. If cancer cells have spread to the lungs, other organs and other bones, there is a chance of killing some or all of those abnormal cells. In Maddie’s case we believe that every bone cancer cell was killed, or she would later have succumbed to the disease. Total cures such as hers almost never happen, but chemotherapy tends to be the best method of buying time. Chemotherapy, as you might imagine, is not inexpensive.
- Radiation: radiation is an excellent adjunct treatment to surgery and chemotherapy. Every added mode of treatment increases your pet’s chances of having more time alive before the cancer takes over. That’s the up side. The down side is that your pet will be anesthetized daily, usually five days each week, and will stay in the treatment facility all week for six weeks, going home only on weekends. There is also substantial cost associated with radiation therapy.
- Pain management: osteosarcoma is a full-thickness disease, meaning it affects the bone from the marrow (the very inside) to the periosteum (the lining of the very outside of the bone). Bang your shin with a hammer and you will understand that there are thousands of pain nerve endings in each square inch of periosteum. Now, stretch that periosteum with a fast-growing cancer and radically disrupt the bone through and through. You have some idea of the level of pain osteosarcoma patients have and the challenge of combining medications that will allow a pet to function through his day, yet control his pain. We are fortunate to live and practice in a time in which we have access to many excellent pain-controlling medications.
I can’t say it enough: Osteosarcoma in dogs and cats is not always an instantaneous death sentence. Those patients with the right set of parameters can survive for a time, possibly a long time, and have good lives for the time they have. It will require a lot of dedication and money.
Your pet’s doctor can discuss the options with you as well as let you know the availability of oncologists and specialty surgeons in your area. He will have a frank talk with you about whether your pet is a candidate for aggressive therapy.