A comprehensive immunophenotypic marker analysis of hairy cell leukemia in paraffin-embedded bone marrow trephine biopsies--a tissue microarray study.

Hairy cell leukemia (HCL) is an uncommon B cell lymphoproliferation characterized by a unique immunophenotype. Due to low number of circulating neoplastic cells and 'dry tap' aspiration, the diagnosis is often based on BM trephine biopsy. We have performed a consecutive immunohistochemical analysis to evaluate diagnostic usefulness of various HCL markers (CD11c, CD25, CD68, CD103, CD123, CD200, annexin A1, cyclin D1, DBA.44, HBME-1, phospho-ERK1/2, TRAP, and T-bet) currently available against fixation resistant epitopes. We analyzed tissue microarrays consisting of samples gained from 73 small B-cell lymphoma cases, including hairy cell leukemia (HCL) (n = 32), HCL variant (HCL-v) (n = 4), B-cell chronic lymphocytic leukemia (B-CLL) (n = 11), lymphoplasmacytic lymphoma (LPL) (n = 3), mantle cell lymphoma (MCL) (n = 10), splenic diffuse red pulp small B cell lymphoma (SDRPL) (n = 2), splenic B cell marginal zone lymphoma (SMZL) (n = 8), and splenic B cell lymphoma/leukemia, unclassifiable (SBCL) (n = 3) cases. The HCL cases were 100% positive for all but 2 (DBA.44 and CD123) of these markers. Annexin A1 showed 100% specificity and accuracy, which was followed by CD123, pERK, CD103, HBME-1, CD11c, CD25, CD68, cyclin D1, CD200, T-bet, DBA.44, and TRAP, in decreasing order. In conclusion, our results reassured the high specificity of annexin A1 and pERK, as well as the diagnostic value of standard HCL markers of CD11c, CD25, CD103, and CD123 also in paraffin-embedded BM samples. Additional markers, including HBME-1, cyclin D1, CD200, and T-bet also represent valuable tools in the differential diagnosis of HCL and its mimics.