Low-grade small B-cell lymphomas: Pathology and differential diagnosis

Haema 2013; 4(2):103-116

by Theodora Papadaki

Haematopathology Department Evangelismos Hospital, Athens, Greece

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The broad group of small B-cell Lymphomas comprises some of the most frequently en- countered lymphomas in routine surgical pathology practice which can be subdivided into three main categories concerning their primary site of involvement: a) primary nodal and leukemic small B-cell lymphomas b) primary splenic small B-cell lymphomas and c) primary extranodal small B-cell lymphomas. The group of primary nodal and leukemic small B-cell lymphomas is highly heterogeneous with many overlapping histological and/or immunohistochemical features. This report analyses the newly available immunohistochemical as well as molecular/cytogenetic markers and thear value: a) in the differential diagnosis between the different entities of small B-cell lymphomas group and b) in the identification of the recently recognized precursor (early) lesions wich do not appear to represent overt lymphomas. The primary splenic small B-cell lymphomas comprise mainly distinct or provisional entities primarily involving the spleen and to a lesser extent other small B-cell lymphomas also involving primarily the lymph nodes. In this review we present the newly defined immunohistochemical and molecular/cytogenetic characteristics of these entities helping to distinguish between: a) the different primary splenic lymphoma subtypes and b) primary splenic B-cell lymphoma from non neoplastic splenic disorders mimicking morphogically and/or immunophenotypically lymphoma. Finally the group of primary extranodal small B-cell lymphomas, mainly represented by extranodal marginal zone lymphoma, of MALT-type, rarely includes cases of primary extranodal mantle cell lymphoma as well as primary extranodal follicular lymphoma. Given the different natural history and prognosis between the above entities a multiparametric diagnostic approach is recommended in order to differentiate between: a) these biologically different lymphoma entities; and b) lymphoma and reactive extranodal lymphoid infiltrates mimicking lymphoma.