Osteosarcomas are common malignancies in large breeds of dogs. Although there has been dramatic progress in their treatment, these therapies often fail, leading to recurrence of the tumour and metastatic spread.
Osteosarcoma of the long bones is the most common malignant tumor of bone in dogs accounting for 85 −90% of primary bone tumors and almost exclusively affects the large and giant breeds such as rottweiler, great Dane, Irish wolfhound, greyhound, Saint Bernard. In general, Dogs with a body weight above 40 kg are more predisposed than smaller dogs. It is believed that osteosarcoma is associated with weight bearing, and rapid bone growth during early development along with bone stress due to weight bearing (possibly resulting in microfractures). Increasing weight and height appear to be important predictive factors for the disease in the dog. Growth hormone has been shown to be present in canine osteosarcoma samples and studies evaluating the role of insulin-like growth factor-1 (IGF-1) and its receptor IGF-1R and hepatocyte growth factor (HGF) and its receptor c-Met in osteosarcoma cell lines and tissues have shown that these factors may contribute to the malignancy.
Sex hormones may also contribute to osteosarcoma risk with intact males and females being reported to be at increased risk. However in the rottweiler neutering before 1 year of age appeared to increase risk of bone sarcoma in both male and female dogs. Breeds reported to be at increased risk of developing osteosarcoma include the doberman, German shepherd, golden retriever, great Dane, Irish setter, rottweiler and Saint Bernard, large sight-hounds such as Irish wolfhound, Scottish deerhound and Borzoi, greyhound, rottweiler and great Dane and Irish wolfhound, Saint Bernard, and Leonberger.
Weight-bearing regions of the long bones (humerus, femur, radius, tibia and ulna) are most often affected, with approximately 25 % of tumors arising in the axial skeleton including the flat bones of the skull, ribs, vertebrae, sternum, and pelvis. Osteosarcomas is an aggressive and invasive tumor that causes local skeletal destruction. Diagnosis is based on physical examination, radiography of the lesion and fine needle biopsy performed in order to identify the type of tumor. They are highly metastatic, predominantly to the lungs with a lower frequency of spread to distant bones, lymph nodes and other soft tissues. Affected dogs suffer from lameness or in some cases with a pathologic fracture of the affected bone.
Treatment includes: surgery (limb amputation or limb-sparing surgery), radiotherapy and chemotherapy. Amputation is a first-line procedure, which increases survival, brings pain relief, thereby delays euthanasia. It completely removes the primary tumor, decreases the risk of postoperative complications, shortens the time of anesthesia and decreases the expense in comparison with the limb-sparing procedure. However, limb-sparing procedures are receiving growing popularity. The bone can be reconstructed with an endoprothesis (metal implant) or cortical allograft. Limb function is preserved in over 80 % of dogs following limb-sparing surgery, however, complications such as infections (in 30–50 % of patients) or implant failure (20–40 %) are relatively common. Moreover, tumor recurrence appears in 15–25 % of cases. As a result this technique is recommended for dogs with compromising neurologic or orthopedic problems, or it can be favorable for owners who refuse to perform limb amputation. In the absence of chemotherapy, the average survival time in dogs receiving amputation alone is approximately 19 weeks. Dogs treated with adjunctive therapy had a prolonged median survival time (307 days) in comparison to those after surgery alone. Dogs with appendicular OSA treated with cisplatin as an adjuvant therapy to amputation or limb-sparing surgery (322 days), than with surgery alone. It is believed that doxorubicin used in OSA treatment is as effective as cisplatin or carboplatin. Alternative chemotherapy protocols include using lobaplatin or ifosfamide. Another attempt to improve chemotherapy’s effectiveness was to compare the effects of two cytostatic drugs given in an alternating schedule. The efficiency of alternating the administration of cisplatin and doxorubicin after amputation was evaluated. 38 dogs treated with combined therapy after amputation had a significantly longer survival time than dogs that were treated with amputation alone, yet the result was still similar to the one achieved during monotherapy which involves carboplatin or doxorubicin.
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