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Background Accurate assessment of the somatic mutational status of clonal immunoglobulin variable region (IgV) genes is relevant in elucidating tumour cell origin in B-cell lymphoma; virgin B cells bear unmutated IgV genes, while germinal centre and postfollicular B cells carry mutated IgV genes. Furthermore, biases in the IgV repertoire and distribution pattern of somatic mutations indicate a possible antigen role in the pathogenesis of B-cell malignancies. Objectives This work investigates the cellular origin and antigenic selection in primary cutaneous B-cell lymphoma (PCBCL). Methods We analysed the nucleotide sequence of clonal IgV heavy-chain gene (IgVH) rearrangements in 51 cases of PCBCL (25 follicle centre, 19 marginal zone and seven diffuse large B-cell lymphoma, leg-type) and compared IgVH sequences with their closest germline segment in the GenBank database. Molecular data were then correlated with histopathological features. Results We showed that all but one of the 51 IgVH sequences analysed exhibited extensive somatic hypermutations. The detected mutation rate ranged from 1·6% to 21%, with a median rate of 9·8% and was independent of PCBCL histotype. Calculation of antigen-selection pressure showed that 39% of the mutated IgVH genes displayed a number of replacement mutations and silent mutations in a pattern consistent with antigenic selection. Furthermore, two segments, VH1-69 (12%) and VH4-59 (14%), were preferentially used in our case series. Conclusions Data indicate that neoplastic B cells of PBCBL have experienced germinal centre reaction and also suggest that the involvement of IgVH genes is not entirely random in PCBCL and that common antigen epitopes could be pathologically relevant in cutaneous lymphomagenesis. [ABSTRACT FROM AUTHOR]

Mature B-cell malignancies stem from B cells transformed at various developmental stages, accounting for the wide range of heterogeneous features observed in the different disease entities. Analysis of the immunoglobulin (Ig) genes can facilitate the identification of the normal B-cell counterpart of lymphomas and leukemias, as Ig genes acquire somatic hypermutation in germinal centers during the immune response to antigen. Therefore, lymphomas that derive from a naïve, pregerminal center B cell lack somatic hypermutation in the clonal Ig gene, whereas germinal center-derived lymphomas, such as diffuse large B-cell lymphoma and follicular lymphoma, display somatic hypermutation of their Ig genes. Furthermore, biases in the Ig variable heavy chain gene repertoire in B-cell malignancies can indicate a possible antigenic influence in pathogenesis. Much work has been accomplished in the past decade to characterize the Ig genes in different lymphoma entities, and the separation of chronic lymphocytic leukemia into two prognostic subgroups in the late 1990s based on the presence or absence of somatic hypermutation led to investigations of Ig genes in larger cohorts of previously uncharacterized entities, such as mantle cell lymphoma. This review will briefly discuss relevant aspects of normal B-cell development, and then focus on what can be ascertained from Ig studies of newly characterized entities, mantle cell lymphoma, hairy cell leukemia, lymphoplasmacytic lymphoma/Waldenström’s macroglobulinemia, and splenic marginal zone lymphoma, from the point of view of cellular origin and variable heavy chain gene restrictions as a sign of antigen involvement. Correlations with gene expression profiling data and the clinical implications of Ig gene studies, when relevant, will be mentioned. The recent evidence that an alternative pathway of gaining somatic hypermutation might exist is also considered, and the implications this has for understanding the cellular origin of B-cell malignancies. [ABSTRACT FROM AUTHOR]