Abstract Objective To evaluate the effects of the concomitant use of proton pump inhibitors (PPIs) and/or antibiotics (Abs) on oncological outcomes in patients with advanced urothelial carcinoma. Patients and methods We retrospectively evaluated 155 patients with advanced urothelial carcinoma who were treated with immune checkpoint inhibitors (ICIs) between August 2015 and April 2021. The concomitant use of PPI or Abs was defined as any PPI or Abs administered within 30 days before ICI initiation and during ICI therapy. The primary outcomes were the effect of PPI and/or Abs use on the objective response rate (ORR) and immune‐related adverse events (irAEs). The secondary outcomes were the effects of PPI and/or Abs use on progression‐free survival (PFS) and overall survival (OS) after ICI therapy analyzed using the inverse probability of treatment weighting‐adjusted Cox regression analysis. Results Of the 155 patients enrolled in the study, 99 (64%) were PPI users and 56 (36%) Abs users. PPI users were associated with a significantly poorer ORR than non‐PPI users (41% vs. 20%, respectively), whereas Abs use was not significantly associated with changes in ORR. The rate of irAEs was not significantly associated with the use of PPIs or Abs. Multivariate inverse probability of treatment weighting‐adjusted Cox regression analysis revealed significantly poorer PFS and OS in PPI users than in non‐PPI users, whereas Abs use was not associated with poorer outcomes. Conclusion The concomitant use of PPI may adversely affect oncological outcomes in patients with locally advanced or metastatic urothelial carcinoma treated with ICI therapy.
