BRAF Inhibitor, Vemurafenib, in Patients With Relapsed or Refractory Hairy Cell Leukemia

Inclusion Criteria: * ≥ 18 years of age * Histologically confirmed classical HCL with one of the following: * Intolerance to purine analogs or considered to be poor candidates for purine analog-based therapy * Failure to achieve any response (CR or PR) to the initial purine analog-based therapy * Relapse ≤ 2 years of purine analog-based therapy * ≥ 2 relapses Histologic confirmation of diagnosis will be performed at MSKCC or a participating site. * Patients who meet the standard treatment initiation criteria, as defined by ANC ≤1.0, Hgb ≤ 10.0 or PLT ≤100K * ECOG performance status of 0-2 * Acceptable pre-study organ function during screening as defined as: Total bilirubin ≤ 1.5 times the upper limit of normal (ULN), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5x ULN, and serum creatinine ≤ 1.5x ULN * Electrocardiogram (ECG) without evidence of clinically significant ventricular arrhythmias or ischemia as determined by the investigator and a rate-corrected QT interval (QTc, Bazett's formula) of \< 480 msec. * For women of childbearing potential, agreement to the use of two acceptable methods of contraception, including one barrier method, during the study and for 6 months after discontinuation of vemurafenib * For men with female partners of childbearing potential, agreement to use a latex condom and to advise their female partner to use an additional method of contraception during the study and for 6 months after discontinuation of vemurafenib * …