Original ArticlesFollicular Dendritic Cell Sarcoma With Indolent T-Lymphoblastic Proliferation Is Associated With Paraneoplastic Autoimmune Multiorgan SyndromeWalters, Matthew MD*; Pittelkow, Mark R. MD†; Hasserjian, Robert P. MD‡; Harris, Nancy Lee MD‡; Macon, William R. MD§; Kurtin, Paul J. MD§; Rech, Karen L.G. MD§Author Information *Aurora Bay Care Medical Center, Green Bay, WI †Department of Dermatology, Mayo Clinic, Scottsdale, AZ ‡Department of Pathology, Massachusetts General Hospital/Harvard Medical School, Boston, MA §Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN 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: Karen L.G. Rech, MD, Department of Laboratory Medicine and Pathology, Division of Hematopathology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905 (e-mail: firstname.lastname@example.org). The American Journal of Surgical Pathology: December 2018 - Volume 42 - Issue 12 - p 1647-1652 doi: 10.1097/PAS.0000000000001158 Buy Metrics Abstract Nonclonal expansions of immature T cells outside of the thymus, termed indolent T-lymphoblastic proliferation (iT-LBP), have been identified in rare lymphoproliferative disorders. We report that iT-LBP is a frequent finding in cases of follicular dendritic cell sarcoma (FDCS), and shows an association with paraneoplastic autoimmune multiorgan syndrome (PAMS). We studied 31 cases of FDCS by paraffin immunohistochemistry using antibodies to CD21, CD23, CD35, clusterin, CXCL13, podoplanin, CD3, CD4, CD8, CD20, CD1a, and TdT. Chart review was performed to characterize the clinical behavior including evidence of autoimmune disease. FDCS occurred in a wide variety of nodal and extranodal sites. Fourteen of 31 (45%) cases contained immature TdT-positive T cells; in 5 cases these cells were numerous and present throughout the tumor. Four of these 5 patients with numerous immature T cells developed autoimmune disease, clinically categorized as PAMS and/or myasthenia gravis. PAMS persisted after tumor resection, causing severe morbidity and mortality. These findings suggest that the neoplastic follicular dendritic cells can recruit or foster the proliferation of immature T cells and that these cells may play a role in mediating PAMS. Recognition of iT-LBP in FDCS is important to avoid misdiagnosis as thymoma or T-lymphoblastic lymphoma, and may predict serious autoimmune complications in some patients. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.