Extensive rib osteosarcoma with intraperitoneal invasion in a small breed dog: Clinical and histopathologic findings

An 11-year-old mixed breed male dog was presented with a thoracoabdominal wall mass of 3-year duration. Initial tentative diagnosis of osteosarcoma was made. Despite chemotherapy treatment, 72 days following the date of presentation, the dog was euthanized. Based upon necropsy and histopathologic findings, the tumor was definitely diagnosed as a combined type osteosarcoma of the rib. At necropsy examination, the tumor extended the left kidney and diaphragm, but distant metastasis was not found. The tumor's weight was 2.3 kg and that was 38.3% of the dog's weight. This case report describes the clinicopathological, computed tomographic, histopathologic and immunohistochemical findings of extensive rib osteosarcoma in a small breed dog.