Given the loss-of-function of TP53 and P27 as well as hyperactivation of PI3K/AKT signaling in HCL [6, 21], we next determined whether BRAF(V600E) mutation together with a knockout of Trp53, p27 or pTEN in mice induced a leukemic syndrome resembling human HCL. The gene discussed is BRAF; the disease is hairy cell leukemia.