Clinicopathological characteristics of ovarian sclerosing stromal tumor with an emphasis on TFE3 overexpression

A sclerosing stromal tumor is a very rare benign sex cord-stromal tumor of the ovary. Because its clinical presentation and imaging findings are similar to those of borderline or malignant epithelial tumors and other sex cordstromal tumors, accurate preoperative clinical diagnosis can be difficult. The aim of this study was to analyze the clinicopathological characteristics of SSTs and examine the immunohistochemical expression TFE3, which has not been studied in SSTs. Our study cohort consisted of 9 patients diagnosed as having SST; the median age was 36 years. Radiologically, SSTs presented as multiseptated cystic masses, mixed echoic masses, pseudolobular masses, solid pelvic masses, or uterine subserosal nodules. In 4 of the 9 cases, the preoperative clinical impression was a borderline or malignant ovarian tumor. SSTs displayed the following histopathological features: 1) relatively well-circumscribed cellular nodules that were randomly distributed in the fibrous or edematous stroma; 2) a characteristic alternating pattern of hypercellular and hypocellular areas; 3) a hemangiopericytoma-like vascular growth pattern in the cellular nodules; 4) bland-looking spindle-shaped cells and round or polygonal cells densely clustered around blood vessels; and 5) red blood cell-containing intracytoplasmic vacuole-like spaces in the tumor cell cytoplasm, possibly indicating epithelioid hemangioendothelioma. Immunohistochemically, the tumor cells exhibited diffuse and moderate-to-strong TFE3 expression in 7 of the 9 SSTs. TFE3 was strongly expressed in the nuclei of round or polygonal cells and lutein cells. In contrast, neither luteinized thecomas nor fibromas appreciably expressed TFE3. In summary, our study describes characteristic histopathological features that may be useful for differentiating SSTs from other sex-cord stromal tumors and demonstrates for the first time that SSTs show strong TFE3 expression. Further investigations are necessary to clarify the role of TFE3 in the development of SSTs.