Extraskeletal osteosarcoma in the duodenum of a cat

A three-year-old, male neutered domestic longhair cat was referred for evaluation of icterus, vomiting, and anorexia. Abdominal ultrasonography revealed a proximal duodenal mass obstructing the common bile duct. The mass was surgically resected, and a cholecystoduodenostomy was performed. The histopathological diagnosis was osteosarcoma. Thoracic radiographs showed no evidence of metastasis, and bone scintigraphy revealed no signs of a primary skeletal osteosarcoma. Four months after surgery, the cat had intermittent vomiting, marked weight loss, and died.