Small B-Cell Lymphomas With and Without Plasmacytic Differentiation

Among all mature B-cell neoplasms, the group of small B-cell lymphomas with or without plasmacytic differentiation encompasses several subtypes in which the neoplastic cells constitute a clonal population of predominantly small lymphocytes. Depending on the specific subtype, these lymphomas may show varying degrees of plasmacytic differentiation. Each subtype in this group is characterized by distinct clinical, morphologic, immunophenotypic, and genetic features which are important for precise diagnosis and classification. The majority of these lymphomas are lymph node based; however, extranodal sites such as bone marrow, peripheral blood, and spleen are frequently involved. Precise classification is crucial given their distinct clinical behavior. For example, mantle cell lymphoma is an aggressive disease that often requires therapy, whereas patients with other small B-cell lymphoma subtypes generally have an indolent clinical course and may survive for many years without therapy. With recent advances in molecular genetics, new knowledge about the biology of these diseases has contributed to the development of more refined diagnostic, prognostic, and therapeutic schemes, many of which have been incorporated in the 2017 revised 4th edition of the World Health Organization’s (WHO) classification of hematopoietic tumors. This chapter will focus on the common small mature B-cell lymphomas providing a practical approach for diagnosis and classification.