Grey zone lymphoid neoplasms with features overlapping between splenic marginal zone lymphoma and hairy cell leukaemia: splenic B-cell lymphoma/leukaemia, unclassifiable

Abstract

The best characterized primary splenic B-cell lymphoma/leukaemias include splenic marginal zone lymphoma (SMZL) and hairy cell leukaemia (HCL). However, there are other primary splenic B-cell neoplasms that do not have the characteristic features of SMZL or HCL. The WHO classification has proposed a provision entity—splenic B-cell lymphoma/leukaemia, unclassifiable (SBLLu) to include the better-defined small B-cell clonal lymphoproliferations involving spleen that do not fall into any of the other types of B-cell lymphoid neoplasms. The recognized provisional entities among SBLLu include splenic diffuse red pulp small B-cell lymphoma (SDRPSBL) and hairy cell leukaemia variant (HCLv). The possibility of SBLLu arises when the spleen shows diffuse red pulp involvement, or when the bone marrow trephine biopsy shows extensive intra-sinusoidal involvement by a small B-cell lymphoma with marked splenomegaly, or when a patient with marked splenomegaly presents with a high white cell count in the peripheral blood without monocytopenia, and with presence of atypical lymphocytes with villous or hairy projections and with prominent nucleoli, and the cells are CD25 negative. These clonal B cells lack IgD and frequently express IgG with or without IgM. They are consistently negative for CD25, Annexin A1, cyclin D1, CD38 and cytoplasmic Ig, and are variably positive for CD76, tartrate-resistant acid phosphatase, CD11c, CD103 and CD123. Distinguishing SDRPSBL and HCLv can pose diagnostic problems. Features favouring SDRPSBL include relatively low lymphocytosis along with leucopenia and thrombocytopenia, lack of a paraprotein and a relatively monomorphic cytology with only a proportion of cells being nucleolated. Features that favour HCLv include high white cell count (average ∼35 × 109/L) and presence of monocytes, prominent and obvious intra-sinusoidal infiltrates in spleen and bone marrow and prominence of cells with nucleoli resembling prolymphocytes.