The alteration of the gut microbiota mediated by proton pump inhibitor (PPI) drugs could be involved in the clinical response associated with immunotherapy [immunocheckpoint inhibitors (ICIs)] in cancer patients. Due to the current controversy in the scientific evidence, it has been proposed to evaluate the correlation between the concomitant use of PPIs and the effectiveness of immunotherapy in a real clinical practice setting. Single-center retrospective cohort study that included patients treated with anti-PD-1 or anti-CTLA4, including nivolumab, pembrolizumab, atezolizumab, or the combination ipilimumab-nivolumab in metastatic neoplastic disease. The clinical effectiveness of ICI, measured in progression-free survival (PFS) and overall survival (OS), was compared between the PPI-use versus PPI-no-use group. PPI-use group was associated with lower PFS [hazard ratio (HR):1.89 (1.38-2.59), P<0.001] and OS [HR: 2.02 (1.45-2.82), P<0.001] versus PPI-no-use group. However, this difference was not observed for pembrolizumab PFS [HR: 1.38 (0.93-2.39), P=0.160] and OS [HR: 1.41 (0.81-2.44), P=0.187]. The study showed significantly lower PFS and OS in the chronic PPI-use group (P<0.001), recent PPI-use group (P<0.001) and concomitant PPI-use group (P=0.001, 0.007) versus PPI-no-use group. However, late PPI use >30 days after the onset of ICI has no significant effect on the efficacy of treatment [HR: 0.92 (0.49-1.70), P=0.791; HR: 1.10 (0.59-2.05), P=0.756]. The concomitant use of PPIs in immunotherapy is associated with worse clinical outcomes compared with the group without PPI use. In addition, the study shows how the late use of PPIs does not have a significant effect on clinical benefit.
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