Prior antibiotics, proton pump inhibitors, and probiotics in patients with extensive stage small cell lung cancer treated with immune checkpoint blockade: A post‐hoc analysis of the phase I/III IMpower 133 trial

Abstract The potential impact of concomitant medications such as systemic antibiotics, proton pump inhibitors (PPIs), and probiotics in patients with extensive‐stage small cell lung cancer (ES‐SCLC) receiving first‐line chemo‐immunotherapy combinations remains unclear. We ran a post hoc analysis of the IMpower133 phase I/III trial, which randomized patients with ES‐SCLC to receive carboplatin/etoposide with either atezolizumab or placebo for 4 cycles, followed by maintenance therapy. We included any systemic antibiotic/probiotic exposure within 42 days prior to treatment initiation and any PPIs treatment within 30 days prior to treatment initiation. We explored the potential prognostic impact of antibiotics, PPIs and probiotics across the atezolizumab/chemotherapy and placebo/chemotherapy arms including the multivariable interaction term between the treatment modality and antibiotics/PPIs/probiotics. The analysis included 198 patients in the atezolizumab/chemotherapy arm and 195 in the placebo/chemotherapy arm. Baseline clinic‐pathologic features were well balanced between the two cohorts, with 17 (8.6%) and 14 (7.2%) patients on antibiotics, 43 (21.7%) and 55 (28.2%) on PPIs, and 3 (1.5%) and 5 (2.6%) on probiotics among the atezolizumab/chemotherapy and placebo/chemotherapy cohorts, respectively. Exposure to antibiotics, PPIs, or probiotics was not associated with overall survival or progression free survival in either cohort. Furthermore, interaction terms between these medications and treatment modalities were not statistically significant. Baseline use of antibiotics, PPIs or probiotics did not influence clinical outcomes in patients with ES‐SCLC treated with first‐line atezolizumab/placebo plus chemotherapy, suggesting that they may not have a notable impact on clinical outcomes and could be considered for use in this patient population when necessary.