6ER-039 Concomitant use of proton pump inhibitors and abemaciclib, palbociclib and ribociclib in breast cancer

<h3>Background and Importance</h3> The impact of concomitant use of proton pump inhibitors (PPIs) and cyclin-dependent kinase 4/6 inhibitors (CDK4/6 inhibitors) has shown contradictory results in the literature. <h3>Aim and Objectives</h3> To evaluate the effect of concomitant PPI use (with PPI (cPPI) and without PPI (sPPI)) on the effectiveness of CDK4/6 inhibitors (abemaciclib (ABE), ribociclib (RIB), and palbociclib (PAL)) in patients with metastatic breast cancer (MBC), hormone receptor-positive (HR+) and HER-2 negative. <h3>Material and Methods</h3> This was a 7-year retrospective observational study (September 2017 to May 2024) including all patients treated with CDK4/6 inhibitors for MBC. Effectiveness was assessed by analysing median progression-free survival (PFS) and overall survival (OS) using Kaplan-Meier analysis. Survival curves were compared with the log-rank test, and qualitative variables were analysed with Pearson’s Chi-squared test using SPSS version 26. <h3>Results</h3> A total of 164 patients were included during the study period (mean age 64.7 years (31–90); ECOG 0–2). Among the patients, 29.9% (n=49) received treatment with ABE (67.3% cPPI; 75.5% (n=37) first-line: 67.6% cPPI), 31.7% (n=52) were treated with RIB (46.2% cPPI; 88.5% (n=46) first-line: 47.8% cPPI), and 38.4% (n=63) underwent treatment with PAL (63.5% cPPI; 74.6% (n=47) first-line: 59.6% cPPI). Dose reductions in cPPI vs. sPPI patients were: ABE 45.5% vs. 50% (p=0.765), RIB 33.3% vs. 46.4% (p=0.337), and PAL 35% vs. 69.6% (p=0.008). Median PFS for first-line cPPI vs. sPPI patients was: ABE 10.8 vs. 7.1 months (p=0.581), RIB 10.9 vs. 20.6 months (p=0.337), and PAL 15.2 vs. 15.7 months (p=0.326). Median OS for first-line cPPI vs. sPPI patients was: ABE 12.2 vs. 5.1 months (p=0.357), RIB 8.9 vs. 9.2 months (p=0.270), and PAL 20.2 vs. 16.8 months (p=0.850). <h3>Conclusion and Relevance</h3> The results suggest that concomitant PPI and CDK4/6 inhibitors use does not significantly impact PFS or OS. However, cPPI patients on PAL required fewer dose reductions, possibly indicating lower drug concentrations. Further prospective studies with larger patient cohorts are needed to confirm these findings. <h3>References and/or Acknowledgements</h3> <h3>Conflict of Interest</h3> No conflict of interest