ABSTRACT
A five-year-old male Doberman pinscher with an oval-shaped mass in the left side of thorax, respiratory distress, and an impairment of the use of the left forelimb was referred to the Faculty of Veterinary Medicine of ShahidChamran University in Ahvaz. Radiographs were taken. The abnormal mass was removed by radical surgery. Histopathological examination confirmed the occurrence of a well-differentiated canine osteosarcoma. The case was re-examined after approximately 15 months, which revealed a large mass in the left side and metastases in the right thoracic wall and lung. The decision was taken to euthanize the patient and a necropsy was performed. The recommended treatment for canine osteosarcoma is the removal of the primary tumor followed by adjuvant chemotherapy, but recurrence is common