Correlation of the BRAF V600E mutation in hairy cell leukaemia with morphology, cytochemistry and immunophenotype.

Hairy cell leukaemia (HCL) has distinct clinical, morphological and immunophenotypic features with no recurrent cytogenetic or molecular abnormalities reported until the recent description of the BRAF V600E mutation in patients with classical HCL. The incidence of this mutation was sought in 27 patients with either classical HCL or HCL variant by an allele-specific PCR approach and findings related to morphology, cytochemistry and immunophenotype. A high degree of correlation was noted between the presence of BRAF V600E and established diagnostic criteria in 26/27 patients with HCL/HCL variant. Detection of the BRAF V600E mutation is therefore a useful adjunct in the differential diagnosis of HCL and HCL variant and highlights the value of a multifaceted approach to the diagnosis of this malignancy.