Original ArticlesRosai-Dorfman Disease of the Pancreas Shows Significant Histologic Overlap With IgG4-related DiseaseTracht, Jessica MD*; Reid, Michelle D. MD*; Xue, Yue MD, PhD*; Madrigal, Emilio MD*; Sarmiento, Juan M. MD†; Kooby, David MD†; Alese, Olatunji B. MD‡; Krasinskas, Alyssa M. MD* Author Information Departments of *Pathology and Laboratory Medicine †Surgery ‡Hematology and Medical Oncology, Emory University, Atlanta, GA Conflicts of Interest and Source of Funding: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article. Correspondence: Alyssa M. Krasinskas, MD, Department of Pathology and Laboratory Medicine, Emory University Hospital, 1364 Clifton Road NE, Suite H180D, Atlanta, GA 30322 (e-mail: [email protected]). The American Journal of Surgical Pathology 43(11):p 1536-1546, November 2019. | DOI: 10.1097/PAS.0000000000001334 Buy Metrics Abstract Rosai-Dorfman disease (RDD) is a rare entity characterized by proliferating S100-positive histiocytes. Originally described in lymph nodes, it can involve extranodal sites. Pancreatic involvement is rare, with <10 cases previously reported. Recent studies demonstrate a possible overlap between RDD and the more common IgG4-related disease (IRD), which could further complicate pathologic diagnosis. We describe distinct morphologic characteristics as well as overlapping histologic features of IRD in 5 cases of pancreatic RDD at our institution and compare these to a cohort of nonpancreatic extranodal RDD cases. All pancreatic cases were mass forming and had spindled patterns of elongated histiocytes with smaller areas of more classical appearing RDD; all cases had areas of storiform fibrosis and dense lymphoplasmacytic infiltrates with no increase in IgG4-positive plasma cells, and all cases had some degree of vasculitis (4 cases had obliterative vasculitis). Thirteen nonpancreatic extranodal RDD cases had dense lymphoplasmacytic infiltrates; most (85%) had some fibrosis with 46% showing storiform fibrosis, 85% had vasculitis with 31% demonstrating obliterative vasculitis and 2 cases had increased IgG4 staining. Extranodal (pancreatic and nonpancreatic) RDD often shows overlapping morphologic features with IRD, including lymphoplasmacytic inflammation, storiform fibrosis with elongated histiocytes and vasculitis. This can create a diagnostic challenge in the pancreas where IRD is more commonly encountered. Pathologists need to be aware that RDD can occur in the pancreas and should include RDD in the differential of any mass forming pancreatic lesion in which morphologic features of IRD are present. Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.