What Now?

 

Osteosarcoma is the most common bone cancer in dogs. It can affect any dog, and seems to be quite prevalent in certain breeds. The cause of bone cancer is not known, although several theories have been postulated. It occurs most often in the long bones, particularly the distal wrist or ankle, or proximal hip or shoulder bones. It can also occur in the skull, ribs, spine and pelvis .

The best defense against this horrible disease is awareness, early detection and treatment. Sadly, many dogs are diagnosed after weeks or months of lameness attributed to sprains, arthritis or other joint problems. In the early stages, routinely prescribed anti-inflammatory medications may provide some pain relief, delaying the diagnosis even further. Persistent lameness may be the only sign of bone cancer. In most cases the diagnosis can be made by x-rays, but other tests can be done in questionable cases.

There are many options once bone cancer is diagnosed. In the past several years we have seen huge progress in the treatment of this disease. Thanks to excellent research, new surgical techniques and various chemotherapy protocols have been developed. Statistically, the longest survival rates are seen with a combination of amputation and chemotherapy. Amputation provides permanent relief of the horrible pain caused by bone cancer. Giant breeds and older dogs can function well after amputation, and most dogs are fully recovered from their surgery within two to three weeks.

Not every dog is a candidate for amputation or chemotherapy. Conservative yet aggressive therapy for non-surgical candidates includes radiation therapy, the use of intravenous or oral bisphosphonates and alternative oral chemotherapy regimens. All bone cancer dogs benefit from a change in diet, reducing carbohydrates which cancer cells need to grow. Holistic medicine is a valuable part of treatment, with the addition of supplements and immune boosters that strengthen the dog's immune system.

Cancer is a word, not a sentence. Never give up. Believe in your dog. Every day is a lifetime. There are no wrong decisions, ever. Anything is possible, you just have to believe. If you, or someone you know, has a dog with bone cancer, please visit the online support group.

You are not alone.

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Types of bone cancers

 

The four primary bone tumors are osteosarcoma (OSA), chondrosarcoma (CSA), fibrosarcoma (FSA), and hemangiosarcoma (HSA). OSA is the most common primary bone tumor. Liposarcoma, rhabdomyosarcoma, plasma cell tumors (solitary plasmacytoma and multiple myeloma), and lymphoma can also involve bone, typically as part of a generalized cancer process.

Osteosarcoma (OSA):
OSA is the most common primary bone tumor, accounting for over 85% of all the bone tumors that occur in limbs (known as appendicular). It is estimated to occur in over 10,000 dogs each year in the US. It can also occur in the spine, jaw, skull and ribs. There is no known cause of OSA. Potential explanations for the development of OSA include repetitive bone injury, previous fractures, underlying bone disease, viral infections, genetic predisposition and previous radiation, but none of these theories have been proven. OSA occurs primarily in large and giant breeds of dogs. Smaller breeds are 20 times less likely to develop OSA, but it can occur. Size and height seem to be more important risk factors than breed. Most dogs afflicted with OSA are either young, between 1 and 2 years of age, or older, between 7 and 9 years of age. OSA develops deep within the bone and becomes progressively more painful as it grows outward and the bone is destroyed from the inside out.

Chondrosarcoma (CSA):
This is the second most common primary bone tumor in dogs and accounts for approximately 5% to 10% of all primary bone tumors. It is a cartilage tumor, usually not as malignant as OSA. It generally occurs on flat bones such as ribs or skull bones, but can occur in the limbs, usually the thigh bone (femur). Symptoms are similar to OSA, and many cases are managed with removal of the tumor whenever possible. Chemotherapy has not been shown to be effective. Recent studies suggest that a specific type of antibiotic, called "fluoroquinolone" may be toxic to the cartilage cancer cells. Further studies are needed to see whether this antibiotic will have a role in treatment of this type of cancer.

Fibrosarcoma (FSA):
This type of bone cancer is rare accounting for less than 5% of all primary bone tumors. This type of cancer occurs primarily in the axial skeleton (jaw bones, facial bones, ribs and vertebrae), but it can occur in the limbs. There are two types of Fibrosarcoma which are central and parosteal. Surgical resection, amputation and limb salvage are the main treatment options. It can be confused with a specific type of OSA called fibroblastic osteosarcoma.

Hemangiosarcoma (HSA):
This type of bone cancer is also rare accounting for less than 5% of all primary bone tumors. It tends to occur in a younger age group and can involve either the limbs or the axial skeleton. There is a higher incidence of metastases, so additional tests such as echocardiogram (ultrasound of the heart) or abdominal ultrasound are usually performed before surgical procedures. Management options include amputation and chemotherapy with doxorubicin (adriamycin) type drugs.

Multilobular Osteochondrosarcoma:
This is an uncommon tumor that develops off the lining of the bone (periosteum). The skull is most commonly involved. Other sites include the pelvis, ribs and hard palate. Symptoms depend on the location of the tumor. Computed tomography scans are often recommended to determine the detailed anatomy of the tumor and involvement of the surrounding structures, particularly when it involves the skull or facial bones. Treatment includes surgical resection and radiation. Location of the tumor, histology of the tumor and evaluation of the surgical margins are important for prognosis and risk of recurrence or metastasis.

Primary Joint Tumors:
Synovial cell sarcomas develop from the cells in joints, bursae and tendon sheaths. There are two types of synovial cell sarcomas: epithelioid and spindle.

Other types of joint tumors include histiocytic sarcoma and malignant fibrous histiocytoma, synovial myxoma and myxosarcoma, OSA, FSA, CSA, HSA, liposarcoma, rhabdomyosarcoma, and undifferentiated sarcoma.

Typically, dogs will present with lameness, pain or swelling around the joint. Biopsy is required for a specific diagnosis. Joint fluid will only rarely show cancer cells. Amputation is the recommended treatment. There is no proven effect of either radiation or chemotherapy, although some studies suggest that doxorubicin-based chemotherapy protocols should be considered.

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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 owners 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. 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 relief of the pain of bone cancer.

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.

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Bone Biopsy

 

Bone Biopsy for Bone Cancer:
There are two types of bone biopsy which are 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:

  • Sample was obtained from reactive bone
  • Not enough samples were submitted
  • The tumor is poorly differentiated and cannot be diagnosed on a small biopsy specimen
  • There is necrosis of the bone
  • The sample was crushed or squeezed during handling, or there was excessive decalcification of the bone specimen
Since the bone biopsy will not diagnose 100% of the cases, and most cases can be diagnosed and treated without a biopsy, in most cases this procedure is not necessary. If the diagnosis is clear, and the dog is a candidate for amputation, the information needed from the specimen can be obtained after the amputation surgery.

If the diagnosis is clear based on xrays, 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 usually not needed to determine an alternative cause of treatment. One must be prepared to amputate if there are complications from the biopsy, so if amputation is being considered anyway, the information needed from the specimen can be obtained after the amputation surgery.

However, there are cases where the diagnosis is not clear based on the appearance of the bone lesion, or when more than one lesion is present (which is uncommon in primary bone cancer). In these cases a biopsy may be recommended to actually help clarify the diagnosis. These decisions should be discussed with the primary veterinarian or with the consulting oncologist.

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