Mutation in the BRAF gene leading to a Val-to-Glu substitution in position 600 of the BRAF molecule (V600E) is probably the driving mutation in hairy cell leukemia [8], and a phase II trial testing the BRAF inhibitor vemurafenib in hairy cell leukemia showed promising results, with response in 25 of 26 patients [9]. This evidence concerns the gene BRAF and hairy cell leukemia.