Review ArticlesMediastinal Germ Cell Tumors: A Review and Update on Pathologic, Clinical, and Molecular FeaturesEl-Zaatari, Ziad M. MD*; Ro, Jae Y. MD, PhD*,†Author Information *Department of Pathology and Genomic Medicine, Houston Methodist Hospital, Houston, TX †Weill Medical College of Cornell University (WCMC), New York, NY The authors have no funding or conflicts of interest to disclose. Reprints: Jae Y. Ro, MD, PhD, Department of Pathology and Genomic Medicine, Houston Methodist Hospital, Weill Medical College of Cornell University, 6565 Fannin Street, Houston, TX 77030 (e-mail: [email protected]). All figures can be viewed online in color at www.anatomicpathology.com. Advances In Anatomic Pathology: September 2021 - Volume 28 - Issue 5 - p 335-350 doi: 10.1097/PAP.0000000000000304 Buy Metrics Abstract Mediastinal germ cell tumors (MGCTs) are the most common extragonadal germ cell tumors (GCTs) and most often arise in the anterior mediastinum with a male predilection. MGCTs also have a predilection for patients with Klinefelter syndrome and possibly other genetic conditions. MGCTs, as GCTs at other extragonadal sites, are thought to arise from germ cells improperly retained during migration along the midline during embryogenesis. Similar to their counterparts in the testes, MGCTs are classified into seminomatous and nonseminomatous GCTs. Seminomatous MGCT represents pure seminoma, whereas nonseminomatous MGCTs encompass pure yolk sac tumors, embryonal carcinoma, choriocarcinoma, mature or immature teratoma, and mixed GCTs with any combination of GCT types, including seminoma. Somatic-type or hematologic malignancies can also occur in association with a primary MGCT. MGCTs share molecular findings with GCTs at other sites, most commonly the presence of chromosome 12p gains and isochromosome i(12p). Treatment includes neoadjuvant chemotherapy followed by surgical resection of residual tumor, with the exception of benign teratomas, which require only surgical resection without chemotherapy. In this review, we highlight and provide an update on pathologic, clinical, and molecular features of MGCTs. Immunohistochemical profiles of each tumor type, as well as differential diagnostic considerations, are discussed. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.