Sex cord stromal tumors and tumors of the paratestis: new and old entities in a landscape of rare tumors

Purpose of review The 5th edition of WHO classification incorporates the most relevant new data available in the literature regarding tumors of the male genitourinary tract. In this review, the authors summarize and critically discuss the most relevant new information regarding tumors occurring in the stromal testis and in the paratestis that will be reported in the new edition of WHO classification of tumors of the male genitourinary tract. Recent findings Signet-ring stromal tumors (SRST) and myoid gonadal stromal tumors (MGST) are two new entities brought in the 5th WHO classification of testicular tumors. All cases of SRST and MGST reported so far have behaved in a benign fashion after resection and whenever possible a conservative surgery is recommended. A future perspective is to aim at creating large multiinstitutional case series to link different morphologic patterns and molecular bases to the biologic behavior of these neoplasms. Another innovation in WHO consists in the inclusion in the group of Sertoli cell tumors of the sertoliform cystadenoma. The sertoliform cystadenoma is localized in the rete testis and it is of unknown origin. It was included in the group of gonadal stromal tumors because of a high morphological and immunohistochemical similarity to the Sertoli cell tumor. Although further studies with long-term follow-up are needed to estimate the main oncologic outcomes in patients with rare gonadal stromal tumors, we highlight the importance of an accurate characterization by molecular and immunohistochemical assays of these entities.