Abstract
A rescued male mixed-breed dog, approximately nine years old, was evaluated due to progressive weight loss and an enlarged abdomen. An ultrasound revealed a large, indeterminate mass with mineral-like margins visible on the radiographs. The animal underwent an exploratory laparotomy, and the mass was excised. Histopathological analysis revealed characteristics consistent with a primary omentum extraskeletal osteosarcoma. This rare neoplasm, originating from mesenchymal cell proliferation and bone matrix production, is highly malignant. It often results in death due to metastasis and local recurrence or necessitates euthanasia post-diagnosis in certain cases.