Multicenter retrospective study of concomitant use of PPIs and CDK4/6 inhibitors for endocrine-resistant metastatic breast cancer

Proton pump inhibitors (PPIs) reduce bioavailabbility of several anticancer drugs. Concomitant use of PPIs with cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors is controversial. A retrospective study at 4 centers in Japan investigated the impact of concomitant PPIs on efficacy of CDK4/6 inhibitors(palbociclib or abemaciclib) for endocrine-resistant metastatic breast cancer. Propensity score matching resulted in two groups of 56 patients receiving CDK4/6 inhibitor with or without concomitant PPIs. Concomitant use of PPIs was not associated with worse progression-free or overall survival. Consistent results were seen for the subgroups receiving palbociclib or abemaciclib. Adverse event incidence and severity were similar in both groups. The authors conclude that the effectiveness of CDK4/6 inhibitors is unlikely to be affected by concomitant PPI use.