Exposure-Response Analysis of Osimertinib in EGFR Mutation Positive Non-Small Cell Lung Cancer Patients in a Real-Life Setting

Background Osimertinib, an irreversible inhibitor of the epidermal growth factor receptor (EGFR) is an important drug in the treatment of EGFR-mutation positive non-small cell lung cancer (NSCLC). Clinical trials with osimertinib could not demonstrate an exposure-efficacy relationship, while a relationship between exposure and toxicity has been found. In this study, we report the exposure-response relationships of osimertinib in a real-life setting. Methods A retrospective observational cohort study was performed, including patients receiving 40 - 80 mg osimertinib as >= 2 line therapy and from whom pharmacokinetic samples were collected during routine care. Trough plasma concentrations (C-min,C-pred) were estimated and used as a measure of osimertinib exposure. A previously defined exploratory pharmacokinetic threshold of 166 mu g/L was taken to explore the exposure-efficacy relationship. Results A total of 145 patients and 513 osimertinib plasma concentration samples were included. Median progression free survival (PFS) was 13.3 (95% confidence interval (CI):10.3 - 19.1) months and 9.3 (95% CI: 7.2 - 11.1) months for patients with C-min,C-pred < 166 mu g/L and C-min,C-pred >= 166 mu g/L, respectively (p = 0.03). In the multivariate analysis, a C-min,C-pred < 166 mu g/L resulted in a non-statistically significant hazard ratio of 1.10 (95% CI: 0.60 - 2.01; p = 77). Presence of a EGFR driver-mutation other than the exon 19 del or L858R mutations, led to a shorter PFS with a hazard ratio of 2.89 (95% CI: 1.18 - 7.08; p = 0.02). No relationship between exposure and toxicity was observed (p = 0.91). Conclusion In our real-life cohort, no exposure-response relationship was observed for osimertinib in the current dosing scheme. The feasibility of a standard lower fixed dosing of osimertinib in clinical practice should be studied prospectively.

Automated summary

This study investigates the exposure-response relationship of osimertinib in a real-life setting and finds no relationship between osimertinib exposure and efficacy, but an association between exposure and toxicity. Furthermore, it discovers the influence of EGFR mutation types on the efficacy of osimertinib.