TdT+ T-Lymphoblastic Proliferation in Castleman Disease

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The concept of indolent T-lymphoblastic proliferation (iT-LBP) was introduced by Velankar et al. 1 as the proliferation of immature terminal deoxynucleotidyl transferase (TdT)+ T cells in extrathymic tissue without the involvement of bone marrow or peripheral blood. 2 Although the histopathologic features and the immunophenotype are similar to T-lymphoblastic lympho-ma (T-LBL), iT-LBP is a benign proliferation of thymocytes that requires no treatment. Here, we report a case of iT-LBP in association with hyaline vascular-type Castleman disease in the retroperitoneum of a Korean female. A 37-year-old woman presented with right lower quadrant pain. Abdominal computed tomography scan demonstrated a well-defined homogeneous enhancing mass in the ret-roperitoneum (Fig. 1A). Laparotomy was performed and the mass was resected. Grossly, the resected mass (6.3×4.8×3.1 cm) was well-demarcated, round, and rubbery-firm. The cut surface was pinkish-yellow and fleshy, exhibiting central fibrosis (Fig. 1B). Microscopically, there was a small amount of proliferation of follicles of various shapes and sizes, and expansion of the inter-follicular regions with sinus obliteration (Fig. 1C). Follicles demonstrated expanded mantle zones with onion skinning, regressed germinal centers with hyperplastic follicular dendritic cells reactive for CD21, radially penetrating blood vessels, and few follicle center cells (Fig. 1D–F). Many follicles contained more than one germinal center. The interfollicular region was filled with hyperplastic high endothelial venules, hyalinizing fibrosis, and an admixture of plasma cells, eosinophils, immunoblasts, plasmacytoid dendritic cells, and lymphocytes. In addition, there were multiple nodular and diffuse areas of lymphoid cell infiltration in the interfollicular and perifollicular regions, which were composed of small-to medium-sized cells with a high nu-clear/cytoplasmic ratio and slightly irregular nuclei with open chromatin and inconspicuous nucleoli (Fig. 2A, B). These cells were immunoreactive for TdT, CD3, CD4, and CD8, but negative for CD20 (Fig. 2C, D). The Ki-67 labeling index was also high (Fig. 2F). Some of the large cells in the interfollicular and perifollicular area appeared similar to dysplastic follicular den-dritic cells; consequently, follicular dendritic cell sarcoma was considered. However, these cells were negative for CD21, CD23, or CD35. Systemic work-up revealed no evidence of lymphoma involvement. Polymerase chain reaction study of the T-cell receptor gamma genes using BIOMED-2 primers failed to produce evidence of monoclonal rearrangement (Fig. 2G). A …