Case ReviewsEpithelioid Trophoblastic Tumor of the Uterus Differential Diagnosis and a Review of Gestational Trophoblastic TumorsZaloudek, Charles J. MDAuthor Information From the Department of Pathology, University of California, San Francisco, CA. Reprints: Charles J. Zaloudek, MD, Department of Pathology, University of California, San Francisco, 1825 Fourth St, Room M2380, San Francisco, CA 94143. E-mail: Charles.firstname.lastname@example.org. The author has no funding or conflicts to declare. AJSP: Review and Reports: March/April 2016 - Volume 21 - Issue 2 - p 93-102 doi: 10.1097/PCR.0000000000000136 Buy Metrics Abstract Choriocarcinoma, placental site trophoblastic tumor, and epithelioid trophoblastic tumor are the main types of gestational trophoblastic neoplasms; mixed types of trophoblastic tumors also occur. Epithelioid trophoblastic tumor is the most recently described type of gestational trophoblastic neoplasia. This rare tumor is composed of epithelioid cells with large atypical nuclei and moderate to abundant clear to eosinophilic cytoplasm, resulting in a carcinomalike appearance. The number of mitotic figures varies, but at least a low level of mitotic activity is present. The tumor cells are proposed to be of chorionic type intermediate trophoblastic cell lineage due to their characteristic p63+/beta-human chorionic gonadotropin and hPL− immunophenotype. Epithelioid trophoblastic tumor must be differentiated from other types of gestational trophoblastic neoplasia such as placental site trophoblastic tumor and choriocarcinoma, from epithelial malignancies such as squamous cell carcinoma of the cervix, and from benign conditions such as placental site nodules. In this report, an epithelioid trophoblastic tumor that occurred in a 40-year-old woman with a 1-year history of abnormal vaginal bleeding is described. The endometrial biopsy contained only small fragments of the tumor, and no mass was detected on imaging studies, so it proved impossible to differentiate between an atypical placental site nodule and an epithelioid trophoblastic tumor until a hysterectomy was performed. The differential diagnosis of epithelioid trophoblastic tumor is discussed, and the clinicopathologic features of placental site nodules and gestational trophoblastic neoplasms are reviewed, emphasizing the features that help pathologists differentiate these conditions from each other. © 2016 Lippincott Williams & Wilkins, Inc.