RAS/RAF path mutation has been identified in 5-9 % of CLL patients. The K601E mutation results in an amino acid substitution at position 601 in BRAF, occurs within the highly conserved motif of the kinase domain. Most mutant BRAF proteins, such as K601E, have increased kinase activity and are transforming in vitro. Preclinical studies suggest that downstream signaling induced by the K601E mutant may be blocked by the BRAF inhibitor, vemurafenib.