Low-Grade Endometrial Stromal Sarcoma
A 61-year-old Japanese woman had recurrent low-grade endometrial stromal sarcoma (ESS) after primary treatment 9 years earlier. Initial and recurrent tumors showed the same configuration that the polycystic part showed in the solid tumor ultrasonographically. The central part of both the initial and recurrent tumors showed typical histologic findings, but bizarre cells were detected in the peripheral layer of the recurrent tumor. They resembled glandular cells, Comet cells of high-grade ESS, fibroblasts, decidual cells, and predecidual endometrial stromal cells at the middle to late secretory phases. The change and differentiation of low-grade ESS by therapy and environment seem to be the same as the differentiation in mesenchymal stem cells. We speculate that recurrence and prognosis of low-grade ESS are related by extrauterine development but not by mitotic activity or DNA content.

Malignant tumors composed exclusively of cells originating from the endometrial stroma are rare. These neoplasms have a variety of histopathologic characteristics and clinical courses, ranging from indolent local growth to rapid extensive progression. Recurrent cases of low-grade endometrial stromal sarcoma (ESS) are especially rare. We report a case of recurrent low-grade ESS that regrew in the left pelvic wall, where the primary tumor had been surgically resected 9 years earlier. The histologic activity of the recurrent tumor was not changed from that of the primary tumor, and tumor aggressiveness was not detected by DNA content.