Diagnosing Osteosarcoma

Symptoms

Bone cancer occurs most often in the bones of the distal radius (above the wrist joint), in the upper arm bone (near the shoulder), in the lower part of the femur (thigh bone) and the upper part of the tibia (the larger of the two leg bones). Less commonly it can appear in the pelvic bones, shoulder blades or spinal bones (vertebrae). The most common symptoms of bone cancer are lameness and pain. Symptoms can develop over a short period of time, or the lameness can be persistent, not responding to conservative treatment for a sprain or joint injury. In some cases, bony swelling can be seen or felt, sometimes by accident. The involved area can be tender to touch, but not always. In other cases, the first sign of bone cancer can be acute pain and lameness from a fracture through the cancerous bone. Less commonly, the first symptoms might be due to spread of the cancer (metastases) to other organs. Other dogs will exhibit loss of appetite, depression or decrease in activity.

Bone cancer can also occur in the skull, facial bones or ribs. Trouble chewing, trouble swallowing, facial swelling or nasal discharge could be signs of bone cancer in the skull or facial bones. A hard lump on a rib could be a sign of bone cancer in the ribs.

In order to diagnose bone cancer (osteosarcoma) you have to think of it. Thinking about it may provide an early diagnosis which could affect the outcome. The disease occurs more commonly in older dogs, the same group that is more likely to have arthritis or ligament injuries. Young dogs with bone cancer are often diagnosed with sprains or ligament problems. Many dogs develop a lameness that is often attributed to some other cause, only to find later on that the real problem is bone cancer.

Anti-inflammatory medications are often prescribed to treat the lameness, even before Xrays are done. Improvement in symptoms does not exclude the diagnosis of bone cancer. The key to early diagnosis is having xrays done early on. Blood work can help exclude other causes of lameness or systemic illness. It should be done as a baseline reference after the diagnosis is confirmed and can be used to monitor for side effects of medications, especially anti-inflammatories. A blood enzyme called “alkaline phosphatase” is sometimes checked to assess prognosis. A normal result is better, but a high level of this enzyme does not necessarily mean the dog will do poorly, and should not be used to defer treatment of the disease.

XRays

The best way to evaluate persistent lameness, pain or swelling is with an xray. Characteristic changes of bone cancer can be seen fairly early on. Classic findings include a “lytic” lesion, where the bone appears to have been eaten away, and is no longer smooth, or a “sunburst” pattern, revealing the tumor as it grows outward toward the periphery of the bone and pushes normal bone out of the way. A fracture can also be seen through the tumor. As a rule, osteosarcoma does not cross the joint line and does not affect the bone on the other side of the joint.

Other causes of pain and lameness can be excluded on the xray as well. While these changes are usually typical of osteosarcoma, the diagnosis may not always be readily obvious. Other types of cancer that can cause “lytic” lesions in bone include chondrosarcoma, squamous cell cancer, or synovial cell sarcoma. In the majority of cases, the primary veterinarian can interpret the xrays and diagnose osteosarcoma. If there is any question about the diagnosis, a formal interpretation by a veterinary radiologist might be helpful. In specific cases, bone scan, CT scan or MRI might provide additional information, but these additional tests are usually not necessary.

Many times clients are told the abnormalities could be due to a bone infection, which can be caused by a fungus or bacteria. The fungal infection most likely to mimic bone cancer is Coccidiodomycosis or “Valley Fever”. This condition is native to the Southwest United States and in rare cases can cause a proliferative bone lesion which is usually not lytic. It is most often accompanied by evidence of infection in other organs, and can affect other bones. Unless the dog has lived in the Southwest, the chances of this particular fungal infection are virtually zero.

There are two forms of bacterial bone infection (osteomyelitis): acute and chronic. There is almost always a history of some kind of trauma to the area: open fracture, gunshot injury, bite wound, previous surgery or soft tissue infection. It can occur when there is bacteria in the bloodstream AND the bone has been damaged someway. Just having bacteria in the blood isn’t enough. There can be swelling, lameness, pain and loss of appetite. Fever is a clue to the diagnosis of osteomyelitis in acute cases, but not in chronic ones. Xray findings include soft tissue swelling, new bone formation that can look spiculated, lysis of bone, thinning of the cortex and even fracture. In some cases the x-rays can be diagnostic but not always.

In these cases the xrays can be confusing, and both bone cancer and infection can present the same way. When there is a really high suspicion of an infection, the veterinarian will do specific blood work and recommend a bone biopsy. The purpose of the biopsy in osteomyelitis is to isolate the organism causing the infection so that proper antibiotic therapy can be prescribed. Antibiotics are typically prescribed for 4-6 weeks if the infection is acute and there is no fracture. If it is chronic and there is seclusion of the infection in a certain area of bone, then surgery is required in addition to long term antibiotics. Fractures can occur and require bone grafts which can fail if the infection is not cleared. Chronic osteomyelitis often causes microabscesses that can actually create a tract from the bone through the skin, which makes diagnosing osteomyelitis easier. Treatment is frustrating and expensive, which is why some vets may recommend amputation.

The Next Step

Most cases of bone cancer can be diagnosed with Xrays and the treatment plan can be decided without further testing. Chest Xrays should be done to determine if visible lung metastases are seen, and to assess the heart if there are underlying medical problems. Whenever feasible, amputation or resection are recommended, and in many cases chemotherapy is also planned. The current statistics show the greatest survival rates with combination amputation and chemotherapy. Even in the presence of lung metastases, some people will proceed with the amputation to provide permanent pain management.

After amputation, the surgical specimen should be sent to Pathology for identification of cell type and confirmation of the type of bone cancer. This information can be useful in determining further treatment, including chemotherapy. In addition, some insurance companies require histologic confirmation of the diagnosis to process claims.

There is no reason to do a bone biopsy to “confirm” what is obviously cancer on the xrays. It can cause additional pain and may result in a pathologic fracture. In some cases, however, the Xrays may not be typical for bone cancer and should be reviewed by a veterinary radiologist. If the diagnosis is still not obvious or if there is more than one bone lesion, the veterinarian may recommend a bone biopsy. If the lesion is in the distal ulna or radius and limb-sparing surgery is being considered, the surgeon doing the limb-spare surgery should be the one doing the biopsy, so that the biopsy tract is contained within the area that will be removed during surgery.

Bone Biopsy for Bone Cancer

There are two types of bone biopsy: open incisional biopsy and closed needle or trephine biopsy. The open method allows for removal of a good sized piece of tissue, which increases the chances of an accurate diagnosis. Bruising on the bone, wound infection, seeding of the surgical site with tumor cells and pathologic fractures are major disadvantages of this technique.

The closed needle (Jamshidi needle) or trephine (Michelle trephine) is preferred, since the incidence of post operative complications is greatly reduced. Even though it provides a smaller specimen, a quick, accurate diagnosis can be made in up to 94% of cases. There might be a slightly lower incidence of pathologic fractures with the Jamshidi needle.

In order to achieve the best results with biopsy, several specimens should be obtained. The biopsies should be taken from the center of the lesion, since bone cancer grows from the inside of the bone (medullary space) to the outside (cortex). If an open incisional biopsy is planned, the incision should be positioned so that the entire area can be completely removed if amputation is later scheduled.

The biopsy can be “negative” or “non-conclusive”. Reasons for this include:

Since the bone biopsy will not diagnose 100% of the cases, and most cases can be diagnosed and treated without a biopsy, there is really very little need for this invasive procedure. If the diagnosis is clear, and the dog is not a candidate for amputation because of other health problems, or because of the location of the tumor, then biopsies are not needed to determine an alternative cause of treatment. One must be prepared to amputate if there are complications from the biopsy, and the information needed from the specimen can be obtained after the amputation surgery.