Bone Cancer in Dogs
Overview
Types of Bone Cancer
Each year over 10,000 dogs are diagnosed with bone cancer in the U.S. 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 percent of all the bone tumors that occur in limbs (known as appendicular). 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 has been proven. OSA occurs primarily in large and giant breeds. Smaller breeds are 20 times less likely to develop OSA. 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 percent to 10 percent 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. Some 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 percent 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: 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 percent 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 Osteosarcoma
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, 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.
