Concomitant Use of Proton Pump Inhibitors and CDK4/6 Inhibitors in Metastatic Hormone-Positive Breast Cancer: A Real-World Cohort Study.

Introduction: Conflicting evidence exists regarding the concurrent use of cyclin-dependent kinase (CDK) 4/6 inhibitors and proton pump inhibitors (PPIs) in the treatment of breast cancer. This study aimed to investigate whether PPI use interferes with the efficacy of CDK4/6 inhibitors.

Methods: This retrospective, multicenter, real-world study included 205 patients with hormone receptor-positive, HER2-negative metastatic breast cancer. Patient data were collected from January 2020 to August 2023. Patients who received either ribociclib or palbociclib, with or without a PPI, were included. Median progression-free survival (mPFS) was estimated using the Kaplan-Meier method, and factors associated with mPFS were analyzed using Cox regression.

Results: Among the patients, 100 received palbociclib and 105 received ribociclib. In the palbociclib group, 40 patients (40%) used a PPI, and 60 (60%) did not. The mPFS was 16.1 months for patients with a PPI versus 22.2 months for those without (p = 0.26). In the ribociclib group, 44 patients used a PPI and 61 did not use a PPI. The median PFS was comparable between patients receiving PPIs and those not receiving PPIs (19.3 months and 20.7 months, respectively). Poor PFS was associated with liver metastasis, brain metastasis, and high Ki-67.

Conclusion: Concomitant use of PPIs with ribociclib or palbociclib did not affect the efficacy of either CDK4/6 inhibitor. PPIs can be administered alongside these medications when clinically indicated.