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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.

Acute myeloid leukaemia (AML) with 3q26 cytogenetic abnormalities is associated with overexpression of EVI1, dysmegakaryopoiesis and poor prognosis. Screening for EVI1 transcripts was performed in 336 cases of AML, including 139 patients with acute promyelocytic leukaemia (APL). Expression was detected in 7 out of 10 cases with and 23 out of 326 without 3q26 abnormalities including one APL case. Among cases lacking 3q abnormalities, detection of EVI1 transcripts was neither associated with characteristic dysmegakaryopoietic features, nor predictive of a poor outcome, indicating that screening will probably not assist in treatment stratification. This study nevertheless demonstrates that deregulation of EVI1, although rare in APL, is a relatively frequent event in AML.