Simultaneous occurrence of fibroblastic osteosarcoma and hypertrophic osteopathy (Marie’s disease) in a German shepherd dog

Osteosarcoma, as a progressive tumor, accounts for approximately 80% of malignant bone tumors in dogs. Since it is a highly metastatic tumor, it develops pulmonary metastasis in the majority of cases. The considerable site preference of the tumor in dogs and the possibility of hypertrophic osteopathy in a number of cases must be considered. Clinical examination of a 12-year female German shepherd dog with lameness, weakness, and cachexia revealed an abnormal thickening in the left forelimb and a severe swelling in the left proximal humerus. Radiographic examinations showed severe swelling in the arm’s soft tissue, proximal humerus osteolysis, and irregular and palisade periosteal reaction in most bones of thoracic and pelvic limbs as well as soft-tissue masses in the thoracic cavity. In postmortem examination, a semi-hard destructive mass extended from the central cavity of humerus to the surrounding soft tissue, pulmonary and splenic metastases were observed. According to microscopic features, the tumoric bone lesion was diagnosed as fibroblastic osteosarcoma. Hypertrophic osteopathy (Marie’s disease) was also diagnosed due to gross characteristics of the forearm and palm along with radiographic findings of the forearm and tibia. This is the first report of simultaneous occurrence of fibroblastic osteosarcoma and Marie’s disease in Iranian dogs.