Proton-pump inhibitors and palbociclib or abemaciclib in endocrine-sensitive breast cancer treatment.

This study aimed to examine the effects of concomitant use of proton-pump inhibitors (PPIs) on the survival outcomes in patients with endocrine-sensitive chemotherapy-naïve advanced breast cancer (BC) treated with palbociclib or abemaciclib. This multicenter, retrospective study was conducted at five hospitals in Japan. Data were collected from consecutive patients treated with palbociclib or abemaciclib in combination with endocrine therapy as first-line treatment for endocrine-sensitive chemotherapy-naïve advanced BC between December 2017 and August 2022. Associations between concomitant PPI use and survival outcomes were analyzed. Among 202 patients, 38 (19%) were concomitant PPI users. In the palbociclib population (n = 123), concomitant PPI use was associated with a trend toward decreased progression-free survival (PFS) and a significant reduction in overall survival (OS; crude hazard ratio [HR], 1.67; 95% confidence interval [CI], 0.86–3.00 and crude HR, 3.51; 95% CI, 1.53–7.64, respectively). In multivariable analyses, consistent results were obtained (adjusted HR, 1.29; 95% CI, 0.66–2.53 and adjusted HR, 3.23; 95% CI, 1.28–7.67, respectively). In contrast, concomitant PPI use did not significantly affect either PFS or OS in the abemaciclib group (n = 79). Concomitant PPI use decreased the efficacy of palbociclib regardless of the formulation, with no such impact observed with abemaciclib.