Exceptions to the rule in hairy cell leukaemia: implications for molecular diagnostics and targeted therapy

Excerpt

Hairy cell leukaemia (HCL) is a rare, B cell malignancy with specific clinical, morphological and immunophenotypic features. Most patients respond well to currently available purine nucleoside analogue (cladribine, pentostatin) therapy attaining prolonged remissions but a significant number harbour residual disease and have a high risk of relapse. Since the initial description of the BRAF V600E mutation in classical HCL [1], it has become apparent that the overwhelming majority of cases possess this mutation, therefore providing a rationale for targeted therapy with BRAF inhibitors in patients with chemotherapy-refractory disease. Exceptions to this rule are rare but, as is often the case, further study of these exceptional cases can provide some novel insights into disease biology. Absence of the BRAF V600E has been described in several patients with classical HCL, particularly in those expressing the IGHV4-34 immunoglobulin rearrangement [2]. …