Primary uterine osteosarcoma presenting synchronously with bilateral breast carcinomas.

Primary uterine sarcomas are infrequent neoplasms and most commonly leiomyosarcomas or endometrial stromal sarcomas. We report a rare case of primary uterine osteosarcoma discovered in a woman in her 60s following staging CT imaging for bilateral breast carcinomas. Examination of the subsequent hysterectomy specimen showed a tumour composed of malignant spindle cells and osteoclast-like giant cells associated with osteoid and neoplastic bone, in keeping with primary uterine osteosarcoma. Distinction of osteosarcoma from the more common carcinosarcoma is important due to the worse prognosis impacting on treatment decisions. In addition, synchronous presentation of this unusual tumour with bilateral breast carcinomas raises the possibility of a mutual genetic pathogenesis.