Osteosarcoma in a Dog: Diagnostic and Therapeutic Aspects

Background: Osteosarcoma, the most common malignant bone tumor in dogs, is characterized by the proliferation of mesenchymal cells with osteoblastic differentiation, which are responsible for producing osteoid. In appendicular cases, clinical manifestations include pain, lameness, and swelling of the affected limb. This tumor is highly aggressive, with a marked tendency for metastasis, primarily to the lungs, highlighting the importance of early diagnosis and comprehensive tumor staging. Treatment typically involves surgical intervention and adjunctive therapies, such as chemotherapy. This study aimed to report a clinical case of osteosarcoma in a dog. Case: A 7-year-old, intact male Rottweiler, weighing 50 kg, was brought to a veterinary hospital with a primary complaint of right pelvic limb lameness. The dog had a 2-month history of mild difficulty moving the same limb. Physical examination revealed crepitus in the distal tibia and fibula of the right pelvic limb, accompanied by localized swelling, pain, and difficulty bearing weight. Blood tests, including a complete blood count and serum biochemistry (alanine aminotransferase and creatinine), showed no abnormalities. Radiographic evaluation of the limb revealed a pathological fracture in the distal diaphysis of the right tibia and fibula, secondary to a proliferative bone lesion. Fine-needle aspiration cytology suggested mesenchymal neoplasia, likely osteosarcoma, with osteomyelitis as a differential diagnosis. Chest radiographs showed no evidence of metastasis, but abdominal ultrasonography revealed a mineralized thrombus in the caudal vena cava, potentially of neoplastic or metastatic origin. Based on the clinical suspicion of osteosarcoma, limb amputation and biopsy were performed. Histopathological analysis confirmed the diagnosis of osteosarcoma, and chemotherapy was recommended for further management. Discussion: Osteosarcoma is a primary malignant bone tumor commonly diagnosed in large and giant dog breeds. It predominantly affects middle-aged to older dogs with high body weights and occurs more frequently in males. The breed, age, sex, and weight of the patient in this case matched the typical predisposing factors associated with this disease. The clinical signs, including lameness, pain, swelling, weight-bearing difficulty, lethargy, and hyporexia, align with those reported in the literature. However, these signs are nonspecific, making definitive diagnosis challenging. Laboratory tests are often unremarkable, though elevated alkaline phosphatase levels may have prognostic value. Radiographic findings in this case revealed hallmark features of a proliferative bone lesion, and fine-needle aspiration cytology provided supportive evidence for an osteosarcoma diagnosis. These findings guided preoperative decision-making. In this case, no overt metastases were identified. While chest radiographs and abdominal ultrasonography did not indicate overt metastases, computed tomography would have been ideal for more accurate staging. Limb amputation remains the most effective method for analgesia associated with primary bone tumors and for delaying or preventing metastatic disease. In this case, amputation was performed, and histopathological analysis confirmed osteosarcoma. Chemotherapy was subsequently recommended to extend survival and manage potential metastases. Keywords: bone neoplasm, bone tumor, canine osteosarcoma, chemotherapy. Título: Osteossarcoma em um cão: aspectos diagnósticos e terapêuticos  Descritores: osteossarcoma canino, neoplasia óssea, tumor ósseo, quimioterapia.