Clinical outcomes of concomitant use of proton pump inhibitors and regorafenib in patients with metastatic colorectal cancer: a multicenter study

130 Background: Tyrosine kinase inhibitors (TKI) are the most common oral drugs in cancer patients. Similarly, proton pump inhibitors (PPI) are commonly used to relieve dyspeptic symptoms in patients with cancer. However, gastric pH levels may affect the absorption of TKI through the gastrointestinal system. However, all TKIs do not have the same chemical structure, and the absorption rate of each TKI depends on their solubility in different gastric pH levels. Limited data is available about the clinical outcomes of concomitant use of PPI and regorafenib in patients with metastatic colorectal cancer (mCRC). We present here the results of the multicenter study following the initial results of our single-center experience. Methods: Patients with mCRC treated with regorafenib were included in this multicenter and retrospective study. Patients prescribed PPI after initiation of regorafenib were assigned to the PPI user group, and the remaining patients were assigned to the PPI non-user group. To exclude immortal time bias, the log-rank test was performed between PPI non-user and all patients. The primary outcome was overall survival (OS), and secondary outcomes were time to treatment failure (TTF) and adverse events (AEs) profile. Results: Two hundred and seventy-two patients from eight cancer centers were included in this study. Most patients were male (59.9%), had liver metastasis (62.1%), and received regorafenib in the third line (52.2%). The median age at the initiation of regorafenib was 60 years (interquartile range (IQR): 51-66)). Eastern Cooperative Oncology Group performance score was 0 or 1 in approximately three out of four patients. The rate of patients with K-RAS mutation was 46.7%. There were 131 (48.2%) and 141 (51.8%) in the PPI user and non-user groups, respectively. The most prescribed PPI was pantoprazole (40.4%). At a median 34.2 months follow-up, the median OS was 6.9 months (95% Confidence Interval (CI): 5.3-8.5) and 7.7 months (95% CI:6.6-8.8) in the PPI non-user and all patients, respectively. No statistical significance was observed between the groups (p = 0.913). The median TTF was 3.3 months (95% CI: 2.6-3.9) and 3.4 months (95% CI:2.9-4.0) in the PPI non-user and all patients, respectively. No statistical significance was observed between the groups (p = 0.651). In the time-dependent covariate Cox regression model, there was no difference between PPI user and non-user groups in OS and TTF (adjusted Hazard Ratio (aHR):0.96, 95% CI:0.74-1.24, p = 0.735 for OS; aHR:0.88, 0.68-1.14, p = 0.354 for TTF). The rates of all AEs were also similar in the PPI user and non-user groups (p = 0.628). Conclusions: To our knowledge, this was the first study evaluating the effect of concomitant use of PPI and regorafenib in patients with mCRC, and no adverse survival and safety outcome was observed with the concomitant use of PPI and regorafenib in those patients.