To the editor: Hairy cell leukemia (HCL) is a chronic, incurable B cell malignancy that presents with splenomegaly, bone marrow infiltration and cytopenias(1). Long remissions are typically achieved with purine analogues such as cladribine, but most cases will relapse and require further therapy. The discovery of the BRAF V600E mutation in almost all cases of HCL(2) has led to the widespread adoption of the BRAF inhibitor vemurafenib for treatment of patients relapsing after cladribine(3-5). Impressive responses are reported; however, relapse is inevitable(5, 6) and hematologists are now faced with a growing number of patients with vemurafenib-resistant HCL. The optimal management of these patients remains unclear.