CD5-positive hairy cell leukaemia

Abstract

Hairy cell leukaemia (HCL) is readily recognized by its distinct clinical presentation (cytopenias, splenomegaly and neoplastic cells with hair-like cytoplasmic projections), characteristic immunophenotype and BRAF p.V600E mutation. They are typically negative for CD5, CD10 and CD23. Rare cases, however, can have aberrant expression of CD5 and/or CD23 which can be confused with chronic lymphocytic leukaemia/small lymphocytic leukaemia (CD5+/CD23+) or mantle cell lymphoma/leukaemia (CD5+/Cyclin D1+). We describe a rare case of HCL with aberrant expression of CD5 that illustrates the importance of clinical, morphological, immunophenotypical and molecular investigations to resolve the diagnostic challenge.