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

Patients will receive vemurafenib at a dose of 960mg orally b.i.d. continuously in cycles of 4 weeks (28 days) as outpatient. A bone marrow aspirate and/or biopsy will be performed after the first cycle for research purposes only. After the completion of the third cycle, a repeat bone marrow aspirate and/or biopsy will be performed for assessment of response and evaluation of MRD. Following the third cycle assessments, patients who achieve complete response (CR) with detectable MRD or partial response (PR) may continue with vemurafenib for up to 3 additional cycles at the treating physician's discretion (Cycles 4-6). Patients who achieve CR without MRD will be observed as part of post-treatment followup, and may be re-treated with vemurafenib after relapse (as per below). Patients who achieve no response (NR) after the initial 3 cycles of vemurafenib will be removed from the study. They will be followed every 3 months as part of posttreatment followup for a total of 12 months.