Rituximab Plus Bendamustine or Chlorambucil for Chronic Lymphocytic Leukemia: Primary Analysis of the Randomized, Open-label MABLE Study

MABLE investigated the efficacy and safety of rituximab plus bendamustine or rituximab plus chlorambucil in fludarabine-ineligible patients with chronic lymphocytic leukemia. Patients received rituximab plus bendamustine or rituximab plus chlorambucil every four weeks for six cycles. Rituximab plus chlorambucil-treated patients without a complete response after Cycle 6 received chlorambucil monotherapy for at least six additional cycles or until complete response. The primary endpoint was complete response rate (confirmed by bone marrow biopsy) after Cycle 6 in first-line patients. Secondary endpoints included progression-free survival, overall survival, minimal residual disease, and safety. Overall, 357 patients were randomized (rituximab plus bendamustine, n=178; rituximab plus chlorambucil, n=179; intent-to-treat population), including 241 first-line patients (n=121 and n=120, respectively); 355 patients received treatment (n=177 and n=178, respectively; safety population). In first-line patients, complete response rate after Cycle 6 (rituximab plus bendamustine, 24%; rituximab plus chlorambucil, 9%; =0.002) and median progression-free survival (rituximab plus bendamustine, 40 months; rituximab plus chlorambucil, 30 months; =0.003) were higher with rituximab plus bendamustine than rituximab plus chlorambucil. Overall response rate and overall survival were not different. In first-line patients with a complete response, minimal residual disease-negativity was higher with rituximab plus bendamustine than rituximab plus chlorambucil (66% 36%). Overall adverse event incidence was similar (rituximab plus bendamustine, 98%; rituximab plus chlorambucil, 97%). Rituximab plus bendamustine may be a valuable first-line option for fludarabine-ineligible patients with chronic lymphocytic leukemia.