A Phase II Study of the BRAF Inhibitor, Vemurafenib, Plus Obinutuzumab in Patients With Previously Untreated Classical Hairy Cell Leukemia

This is a multi-center, open label, single arm, phase II trial of the oral BRAF inhibitor, vemurafenib, plus obinutuzumab in patients with previously untreated HCL. A Simon mini-max two-stage design will be employed to assess the efficacy of the combination treatment of vemurafenib and obinutuzumab. In the first stage of the protocol, 9 patients will be treated. If fewer than 6 CRs are seen among the first 9 patients, the study will be closed for lack of efficacy. If at least 7 patients respond to the treatment, then an additional 19 patients will be accrued to the second stage, for a total of 28 patients. Eligible patients will receive vemurafenib at a dose of 960mg orally twice daily (b.i.d.) continuously in cycles of 4 weeks (28 days) for a total of 4 cycles. Obinutuzumab will be administered concomitantly with vemurafenib starting at cycle 2 of treatment in cycles of 4 weeks. Obinutuzumab infusions will be administered at 1000mg per day on days 1, 8 and 15 during the cycle 2 and 1000mg per day every 4 weeks during the cycle 3 and 4 of treatment. After the completion of the treatment (i.e. after 4 cycles), a bone marrow aspirate and biopsy will be performed for assessment of response and evaluation of minimal residual disease (MRD). In case of certain defined toxicities, dose reductions of vemurafenib by 50% (480mg b.i.d.) or interruptions of up to 15 days are permitted. If additional dose reduction is required, vemurafenib may be reduced to 240mg oral b.i.d.

Inclusion Criteria: * Patients must be \>/= 18 years of age * Histologically confirmed classical HCL by the enrolling institution * Has not received any prior therapy for the disease * Patients who meet the standard treatment initiation criteria, as defined by ANC \