This article reviews the most typical follicular dendritic cell (FDC) patterns displayed by early lymphomas involving follicles. In in situ follicular lymphoma, FDCs form a well-developed round (spherical) dendritic meshwork with a sharp outline. Other patterns that can be seen include contracted/distorted/disintegrated FDC meshworks. In early mantle cell lymphoma with mantle zone pattern, FDCs compose an ill-outlined and loosely arranged “centrifugal” meshwork. In marginal zone lymphoma, the FDC meshwork forms a relatively well-developed nodular meshwork with irregular outlines. In nodular lymphocyte predominant (LP) Hodgkin lymphoma, LP tumor cells are localized within an environment with prominent FDC meshwork and rare or absent LP cells outside the nodules. In angioimmunoblastic T-cell lymphoma (AITL), scattered regressed germinal centers are usually noted, although hyperplastic germinal centers are seen during the early stages of the disease (EAITL). Identifying the FDC meshwork, mainly in association with blood vessels, constitutes one of the most typical findings of the disease. In conclusion, the morphologic pattern of the FDC meshwork in early lymphomas of follicular origin is heterogenous and differs according to the lymphoma subtypes. These FDC patterns are recognizable in the most typical cases when the lymphoma is in its early stage and still maintains a follicular/nodular pattern of growth. The FDC patterns seen in the CD21 and CD23 stains contribute to the recognition of early stages of lymphomas involving follicles. Conversely, tumor cell immunostains for BCL2, cyclin D1, and other stains form the basis for the definition of lymphoma subtypes.
*Department of Pathology, Centro di Riferimento Oncologico Aviano, Istituto Nazionale Tumori, IRCCS, Aviano
†Department of Diagnostic Pathology and Laboratory Medicine, Fondazione IRCCS, Istituto Nazionale Tumori, Milano, Italy
This paper is based on the study of lymphomas of follicular origin diagnosed by the authors during a 20-year period (from 1986 to 2005) at the Centro di Riferimento Oncologico of Aviano, Italy. The paper is also based on the observation of early neoplastic lymphoid lesions diagnosed by one of the authors (A.C.) from 2010 to 2013 at the Centro di Riferimento Oncologico of Aviano, Italy. All cases were diagnosed and studied by combining H&E and immunohistochemical stainings. Selected subsets of these cases were studied by molecular genetics.
This work was supported in part by an Institutional grant to A.C. from the Centro di Riferimento Oncologico of Aviano for an intramural project on “Molecular Medicine”. The authors have no funding or conflicts of interest to disclose.
Reprints: Antonino Carbone, MD, Department of Pathology, Centro di Riferimento Oncologico Aviano, Istituto Nazionale Tumori, IRCCS, Via F. Gallini 2, 33081 Aviano, Italy (e-mail: firstname.lastname@example.org).