An Update on the Diagnosis, Grading, and Staging of Appendiceal Mucinous NeoplasmsValasek, Mark, A., MD, PhD*; Pai, Reetesh, K., MD†Advances In Anatomic Pathology: January 2018 - Volume 25 - Issue 1 - p 38–60 doi: 10.1097/PAP.0000000000000178 Review Articles Buy Abstract Author InformationAuthors Article MetricsMetrics Despite advances in our understanding of appendiceal mucinous neoplasms and their relationship to the pseudomyxoma peritonei syndrome, the classification of mucinous tumors of the appendix is still confusing. This review will provide an update on the various classification systems that have been recently proposed for appendiceal mucinous neoplasia, with a particular emphasis on how to handle and report the histologic findings for these tumors using the newly published Peritoneal Surface Oncology Group International (PSOGI) and American Joint Committee on Cancer (AJCC) eighth edition guidelines. A simplified approach to diagnostic reporting of appendiceal mucinous neoplasms based on the 3-tier AJCC grading scheme is detailed and specific criteria for assessing grade in appendiceal mucinous neoplasia will be outlined. In addition, histologic mimics of appendiceal mucinous neoplasia and how to distinguish these mimics from mucinous neoplasia will be discussed. Finally, despite improvements in diagnostic terminology, significant challenges in classifying appendiceal mucinous neoplasia persist and diagnostic strategies will be detailed to assist practicing pathologists in these challenging scenarios. *Department of Pathology, University of California, San Diego, CA †Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, PA The authors have no funding or conflicts of interest to disclose. Reprints: Reetesh K. Pai, MD, Department of Pathology, Presbyterian Hospital, University of Pittsburgh, 200 Lothrop Street, Room A-610, Pittsburgh, PA 15213 (e-mail: email@example.com). All figures can be viewed online in color at www.anatomicpathology.com. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.