ReviewsEndometrial Stromal Neoplasms Updates in Classification and Common Diagnostic DilemmasLadwig, Nicholas MD; Garg, Karuna MDAuthor Information From the Department of Pathology, University of California, San Francisco, CA. Reprints: Karuna Garg, MD, Department of Pathology, University of California, San Francisco, 1825 4th St, M-2356, San Francisco, CA 94158. E-mail: Karuna.Garg@ucsf.edu. The authors have no funding or conflicts to declare. AJSP: Review and Reports: March/April 2016 - Volume 21 - Issue 2 - p 73-81 doi: 10.1097/PCR.0000000000000133 Buy Metrics Abstract The classification of endometrial stromal tumors has evolved and changed over the years. The initial classification system divided endometrial stromal sarcomas into low grade and high grade. The 2003 World Health Organization (WHO) classification eliminated the category of high-grade endometrial stromal sarcoma (ESS), and stromal sarcomas were divided into low-grade ESS and undifferentiated endometrial sarcoma. The most recent 2014 WHO classification has reintroduced the category of high-grade ESS, such that endometrial stromal neoplasms are now divided into endometrial stromal nodule, low-grade ESS, high-grade ESS, and undifferentiated uterine sarcoma. In this review, we will discuss the rationale behind these changes. We will also describe the morphologic features, immunohistochemical profile, and clinical features of the various stromal tumors, with particular emphasis on high-grade ESS. Finally, we will discuss briefly the common diagnostic dilemmas and differential diagnoses pertinent to endometrial stromal tumors. © 2016 Lippincott Williams & Wilkins, Inc.