Splenic B-cell lymphoma/leukemia, which is unclassifiable, includes low-grade B-cell lymphoproliferative disorders that do not fit into any other splenic lymphoid neoplasm based on current WHO classification. Presently, two provisional entities, splenic diffuse red pulp small B-cell lymphoma (SDRPL) and hairy-cell leukemia variant (HCL-v), are the most recognizable members of this group. SDRPL is an uncommon malignancy representing less than 1% of all non-Hodgkin lymphomas. Frequent clinical manifestations include splenomegaly and lymphocytosis. SDRPL is currently considered a diagnosis of exclusion and requires clinical and paraclinical correlation, including blood smear, bone marrow and spleen morphology, and the correct immunophenotype (typically positive for CD20, DBA.44, and IgG; and negative for CD5, CD10, CD23, CD43, annexin A1, CD11c, CD25, CD103, and CD123), and cytogenetic findings. Cyclin D3 is expressed in the majority of SDRPL in contrast to other types of small B-cell lymphomas. HCL-v is a less common disease accounting for 0.4% of all chronic lymphoproliferative disorders. It resembles classical HCL and SDRPL by diffusely infiltrating the splenic red pulp but is considered biologically unrelated. Splenomegaly and atypical lymphocytosis without monocytopenia are common. Distinguishing features of HCL-v include morphology, immunophenotype (the absence of CD25, CD200, CD123, annexin A1, and TRAP), genotype (wild-type BRAF), and prognosis.
Part of the book: Lymphoma