A Case Report of Proximal Radioulnar Osteosarcoma in a Great Dane Dog.

Osteosarcoma is the most common primary malignant bone tumor in dogs, characterized by aggressive local invasion and early metastatic potential, most frequently affecting the appendicular skeleton of large and giant breeds. This report describes a rare case of proximal radioulnar osteosarcoma in a 3.5-year-old intact male Great Dane that presented with progressive left forelimb lameness, swelling distal to the elbow, and weight loss. Radiographic examination revealed an aggressive mixed lytic-proliferative lesion involving the proximal radius and ulna, with distinct margins and no radiographic evidence of pulmonary metastasis. A definitive diagnosis of proximal radioulnar osteosarcoma was established by histopathological examination following forelimb amputation with scapulectomy. The dog underwent surgery and showed good postoperative recovery, with no evidence of recurrence during a 6-month follow-up period. Adjuvant chemotherapy was recommended to prevent metastasis, but the owner's financial constraints did not allow for this treatment. This case highlights the importance of early recognition, comprehensive diagnostic evaluation, and timely surgical intervention in managing canine osteosarcoma, particularly at uncommon anatomical sites.