Hairy cell leukemia (HCL) is an uncommon B-cell neoplasm uniquely characterized by a high prevalence of the BRAFV600E mutation, which leads to constitutive activation of the mitogen-activated protein kinase (MAPK) pathway.1 In fact, the BRAFV600E point mutation is identified in nearly all cases of HCL; however, it is absent in HCL variant (vHCL) and rare in other B-cell neoplasms.2,3 Notably, in contrast to melanoma or other BRAF mutant solid tumors, HCL exhibits very few other mutations, potentially explaining the high response rates observed in patients treated with mutant BRAF-targeted agents, such as vemurafenib.