Hairy cell leukaemia (HCL) is an uncommonly encountered chronic B-cell malignancy. HCL is frequently diagnosed after an incidental finding of pancytopenia with many patients asymptomatic. The classical immunophenotype of HCL includes overexpression of B cell markers CD19, CD20 and CD22 and co-expression of CD11c, CD25 and CD123. Other markers such as CD5 and CD10 are generally negative but May be positive in approximately 10-20% of HCL cases. Simultaneous occurrence of HCL and another B cell lymphoproliferative disorder (BLPD) is rare. In this case study we describe a 44-year- old male with persistent neutropenia WHO was ultimately diagnosed with a dual pathology involving both CD10+ HCL and a CD10-/CD5- BLPD. Each of the aberrant populations displayed distinct morphological and immunophenotypic profiles.

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