ABSTRACT
Diffuse large B-cell lymphoma (DLBCL) is the most common type of lymphoma, with an annual U.S. incidence of >25,000 cases (it accounts for approximately one-third of the total number of adult non-Hodgkin lymphoma patients). DLBCL may occur in nodal and extranodal sites and is characterized by a marked degree of morphologic, genetic, and clinical heterogeneity [1–8]. The WHO classification divides DLBCL into several morphologic and clinical variants: DLBCL, not otherwise specified (centroblastic, immunoblastic, and anaplastic variants; Figure 14.1), T-cell-/histiocyte-rich large B-cell lymphoma (THRLBL), primary large B-cell lymphoma of the central nervous system (CNS), EBV+ DLBCL, and primary cutaneous large B-cell lymphoma, leg type (C-DLBCL-LT [9], with the centroblastic variant being the most frequent type (>80%). Other lymphomas of large B-cells include primary mediastinal (thymic) large B-cell lymphoma (PMBL), intravascular large B-cell lymphoma (IVLBCL), lymphomatoid granulomatosis (LyG), ALK+ large B-cell lymphoma, plasmablastic lymphoma (PBL), large B-cell lymphoma arising in HHV8-associated multicentric Castleman disease, and primary effusion lymphoma (PEL). The majority of DLBCLs are positive for CD45 and B-cell markers (CD19, CD20, CD22, CD79a, and PAX5). A subset of DLBCL expresses CD5 (de novo CD5+ DLBCL).
