Recently Described and Clinically Important Entities in Testis Tumors: A Selective Review of Changes Incorporated Into the 2016 Classification of the World Health Organization.

CONTEXT.—: In 2016 the World Health Organization published a revised classification of testicular neoplasms based upon advances in understanding their pathogenesis and molecular biology. The rationale for this revision and additional clinically relevant observations were the topics of a talk given to the Houston Society of Clinical Pathologists in April 2017. This paper summarizes that talk. OBJECTIVE.—: To summarize and explain the most important changes to the classification of testicular neoplasms in the World Health Organization 2016 revision. DATA SOURCES.—: Peer-reviewed published literature and contributions by individuals with expertise in this area that were also reviewed by genitourinary pathologists. CONCLUSIONS.—: Most changes occurred in the germ cell tumor classification, including replacement of the terms intratubular germ cell neoplasia unclassified and carcinoma in situ by germ cell neoplasia in situ; subdivision of the tumors into 2 main categories, those derived from germ cell neoplasia in situ and those not derived from germ cell neoplasia in situ; distinction of germ cell neoplasia in situ from germ cells with delayed maturation and pre-germ cell neoplasia in situ; expansion of the trophoblastic tumor category to include epithelioid trophoblastic tumor and cystic trophoblastic tumor; and substitution of spermatocytic tumor for spermatocytic seminoma and its placement in the non-germ cell neoplasia in situ group. Other revisions included eliminating sclerosing Sertoli cell tumor as a distinct entity; the recognition of intratubular hyalinizing Sertoli cell tumor; and acceptance of the role of undifferentiated gonadal tissue in the pathogenesis of gonadoblastoma.