The median progression-free survival was 9.2 months ( 95 % confidence interval [ CI ] , 7.5 to not estimable ) with palbociclib-fulvestrant and 3.8 months ( 95 % CI , 3.5 to 5.5 ) with placebo-fulvestrant ( hazard ratio for disease progression or death , 0.42 ; 95 % CI , 0.32 to 0.56 ; P < 0.001 ) .