A Study of Vemurafenib and Obinutuzumab Compared to Cladribine and Rituximab in People With Hairy Cell Leukemia (HCL)

Inclusion Criteria: * Patients must be ≥ 18 years of age * Histologically confirmed classical HCL by the enrolling institution * Presence of BRAF V600E mutation as confirmed by PCR, NGS or immunohistochemistry. If patient is known to have negative BRAF mutation, repeat testing is advisable as well as discussion with the main study principal investigator. * Has not received any prior therapy for the disease * 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 and cladribine, and 18 months after discontinuation of rituximab and obinutuzumab * 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 a…