Hairy Cell Leukemia, Hairy Cell Leukemia Variant, and Splenic Diffuse Red Pulp Small B-Cell Lymphoma

Hairy cell leukemia (HCL) and hairy cell leukemia-like neoplasms including HCL variant (HCL-V) and Splenic diffuse red pulp small B-cell lymphoma (SDRPL) are a group of small mature B-cell lymphomas that often involved the spleen, blood, and bone marrow. HCL accounts for only 2% of lymphoid leukemias and HCL-V and SDRPL are even rare. HCL shows characteristic morphology of kidney-bean-shaped nuclei and abundant clear cytoplasm with cytoplasmic hairy projection and phenotypically coexpresses CD19, CD20, CD11c, CD25, and CD103. Nearly 100% of patients with HCL harbor BRAF V600E mutation. Given the differences in infiltrating pattern, phenotype, clinical course, and molecular profiles, both HCL-V and SDRPL are subcategorized under splenic B-cell lymphoma/leukemia, unclassifiable as provisional entities according to the 2016 World Health Organization (WHO) classification. The clinicopathologic features of all rare lymphomas involving the spleen will be discussed in this chapter.