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A case of low-grade ovarian stromal sarcoma in a postmenopausal woman is described. Although pelvic recurrences of the tumor followed 5 and 7 years after the original surgery, the patient has remained well and without evidence of tumor 3 years since the last operation. Histopathologic, electronmicroscopic, and hormonal studies are described. There was evidence of estrogenic stimulation by the theca elements of the tumor in this patient. Cases previously reported in the world literature as malignant thecoma were analyzed, and most of them were considered inadequately documented; indeed most of them were probably either sarcomatoid granulosa cell tumors, stromal sarcomas, or fibrosarcomas. If a thecoma ever becomes malignant, the tumor cells dedifferentiate so that they cannot be recognized any longer as theca cells; instead, they proliferate as a stromal sarcoma or fibrosarcoma. It is proposed, therefore, that the term "malignant thecoma" not be used. On the other hand, very rare malignant ovarian stromal tumors do exist, consisting of undifferentiated stromal cells, fibroblasts, and theca cells, which can show evidence of hormonal activity.

A case of malignant thecoma has been presented. Five previously reported cases have been reviewed and only three of these have criteria acceptable for malignant tumors. The incidence of malignancy in theca-cell tumors is approximately 3 per cent.