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Immunodeficient patients are at an increased risk for developing lymphoproliferative disorders (LPD), including lymphomas. The World Health Organization (WHO) classification recognizes four clinical settings associated with the development of immunodeficiency-related LPDs: (1) primary immune disorders, (2) HIV infection, (3) iatrogenic immunosuppression following solid organ or allogeneic bone marrow transplantation (posttransplant lymphoproliferative disorder [PTLD]), and (4) methotrexate therapy, usually for an autoimmune disorder.1 These lesions are highly heterogeneous, largely due to the various underlying causes of the different immunodeficiencies; however, they share several features (see Table 34-1). In most instances, the LPD are related to Epstein-Barr virus (EBV or HHV-4) infection, and thus, in situations where immunocompetence can be reestablished, these EBV-driven proliferations may regress. However, the development of secondary genetic structural alterations in oncogenes and tumor suppressor genes, not all of which have been defined, results in transformation to a neoplastic process that is no longer responsive to immune modulation. [ABSTRACT FROM AUTHOR]

B-cell non-Hodgkin's lymphomas (B-NHLs) represent a heterogeneous group of neoplasms with respect to their clinical manifestations, histopathologic features, and biological behavior. The now widely utilized World Health Organization (WHO) classification scheme incorporates our current knowledge of the clinical and pathological features of B-cell neoplasms, and categorizes them into distinct entities (Table 1).1,2 It is now generally accepted that B-NHLs arise from neoplastic transformation of B-cells at specific stages of differentiation, although the normal counterparts for some B-NHLs have not been clearly delineated (e.g. hairy cell leukemia). Furthermore, some entities, such as chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), appear to resemble more than one B-cell differentiation stage. Nevertheless, a basic understanding of B-cell differentiation stages and their associated immunophenotypic characteristics facilitates accurate diagnosis and appropriate management of B-NHLs. [ABSTRACT FROM AUTHOR]