The most common grade 3 or 4 adverse events in the palbociclib-fulvestrant group were neutropenia ( 62.0 % , vs. 0.6 % in the placebo-fulvestrant group ) , leukopenia ( 25.2 % vs. 0.6 % ) , anemia ( 2.6 % vs. 1.7 % ) , thrombocytopenia ( 2.3 % vs. 0 % ) , and fatigue ( 2.0 % vs. 1.2 % ) .