Hairy cell leukaemia (HCL) is an uncommon, chronic B cell leukaemia, first reported as a distinct entity in the 1950s.12 HCL accounts for 2% of lymphoid leukaemias, with a male predominance and median age at diagnosis of 58 years. Classical HCL and its variant form (HCL‐V) are now regarded as separate entities,3 with different cytological, haematological and immunophenotypic features. BRAF V600E mutation, present in virtually 100% of cases of classical HCL,4 is regarded as a disease‐defining event, and is absent in HCL‐V.

Advances in management of classical HCL, from use of interferon in the 1980s, to purine analogues in the 1990s, monoclonal antibodies in the 2000s and BRAF inhibitors in the current decade, have resulted in excellent prognosis, with the majority of patients achieving long‐lasting remissions and prolonged survival.56 There remains no clear optimal treatment for HCL‐V, which is one‐tenth as common as classical HCL, with a 5 year survival rate of 57%.7 Advances in diagnostics and treatment necessitate an update of the 2012 BSH guidelines.8

Declaration of Interests

The BSH paid the expenses incurred during the writing of this guidance. None of the authors had conflicts of interest to declare. All authors have made a declaration of interests to the BSH and Task Force Chairs which may be viewed on request.