Treatment with obinutuzumab-chlorambucil or rituximab-chlorambucil , as compared with chlorambucil monotherapy , increased response rates and prolonged progression-free survival ( median progression-free survival , 26.7 months with obinutuzumab-chlorambucil vs. 11.1 months with chlorambucil alone ; hazard ratio for progression or death , 0.18 ; 95 % confidence interval [ CI ] , 0.13 to 0.24 ; P < 0.001 ; and 16.3 months with rituximab-chlorambucil vs. 11.1 months with chlorambucil alone ; hazard ratio , 0.44 ; 95 % CI , 0.34 to 0.57 ; P < 0.001 ) .