Even though osteosarcoma type cancer accounts for only 5% of all dog tumors, it accounts for 80-90% of malignancies involving the bone. Treatment often requires amputation of the affected limb together with chemotherapy to provide temporary relief from this very aggressive disease. Producing lameness relatively quickly, by the time the tumor is discovered in the limb, the cancer has already spread.
Aggressive Dog Bone Cancer
Although osteosarcoma can affect the bones of the spine, ribs or skull, it is most prevalent to the bones of the limbs way from the elbow and close to the knee or in the "wrist" or shoulder, accounting for 75 to 80% of the cases. As the tumor progresses, there is more pain and swelling causing dog lameness, often the first symptom a dog owner notices. Originating deep with the bone itself, osteosarcoma becomes progressively more painful as the tumor grows outward, destroying bone from the inside out and replacing it with tumorous bone. Tumorous bone being weaker than normal bone can result in bone fractures caused by minor injuries. These pathologic fractures will not heal despite "casting" the break or performing any surgical procedures.
Treating Osteosarcoma
A physical examination, blood work, X-rays of the bone and lungs and a biopsy is necessary to determine whether osteosarcoma is present since other bone tumors, as well as fungal or bacterial infections, can cause the same lesions. Lung x-rays will determine if the cancer has spread to the lungs, which occurs in approximately 90% of all new diagnoses. Dog often will cough or gag when the cancer has spread to the lungs.
Limb-sparing procedures, such as a bone graft, may be optional; however, amputation is usually the only treatment available. Limb-sparing procedures can only be done in cases when no muscles are involved, where no more than 50% of the bone is involved and when the tumor is located at the lowest part of the leg. Recovery can be complicated by bone implant rejections and fractures. The source of pain and the source of spreading the cancer is eliminated by removing the tumor. Radiation therapy can control the pain.
A bone graft from a bone bank or with a "re-growing bone" technique called "bone transport osteogenesis" can also replace tumorous bone. The joint nearest the tumor can also be fused and therefore cannot be flexed.
Chemotherapy
Chemotherapy is usually begun immediately after amputation to reduce the possibility of the spread of the cancer and to relieve pain. Recovery from surgery and the adaptation to life as an amputee can be event free and quick. Carboplatin and cisplatin are the most successful drugs available; however, carboplatin is safer though more expensive. Sometimes doxorubicin is combined with cisplatin. The selection of medications depends upon the advantages and disadvantages of each medication. Pain relief can be found with tramadol, gabapentin, amantidne or non-steroidal anti-inflammatory (NSAID) medications such as rimadyl, deramaxx, ectogesic, metacam or a combination of these drugs.
Median survival rates vary but are often less than one year; however, some cancer victims survive a year or longer.