CDK4 and Hypokalemia: Grade ≥ 3 TRAEs was comparable with the other phase I trials of CDK4/6 inhibitors, with the exception of increased GGT and hypokalaemia.2-4 The PALMIRA study showed the overall incidence of increased GGT was 4.4% in 135 patients treated with endocrine therapy combined with palbociclib; 3 patients (2.2%) and 1 patient (0.7%) had grade 3 and 4 increased GGT.5 In contrast, increased GGT was observed in only 1 of 60 patients (1.7%) treated solely with endocrine therapy and was categorized as grade < 3.