Primary osteosarcoma of the ovary. A case report.

A case of primary osteosarcoma arising in the left ovary of a 75-year-old female is described. The chief complaint was a sensation of lower abdominal mass. An abdominal plain film showed a large calcified mass in pelvic region, and a preoperative diagnosis of "ovarian fibroma" was made. The excised tumor was divided into 4 pieces, resembling an oyster shell. Microscopically, the tumor fragments were composed of compact bone or woven bone with surrounding atypical osteoblasts and osteoclasts. The tumor was partly composed of numerous spindle cells with malignant osteoid or atypical chondroid formation, and diagnosed as "osteosarcoma". The cystic part of the lesion was lined with a single layer of columnar cells, but the tumor contained no other germ elements or stem cells, or malignant epithelium. Therefore, it is doubtful that this tumor originated from teratoma or malignant mixed mesodermal tumor, and we conclude that this ovarian osteosarcoma arose through a neoplastic change in ovarian stromal cells. The patient died 4 months after surgery due to intra-abdominal and intrathoracic dissemination of the tumor.