Background and Importance Osimertinib, a third-generation irreversible tyrosine kinase inhibitor of both activating EGFR mutations and resistance-associated T790M point mutation, was approved for treating advanced non-small cell lung cancer (NSCLC).

Aim and Objectives The aim of this study was to investigate the factors predictive of clinical outcome in advanced NSCLC patients receiving osimertinib treatment.

Material and Methods We conducted a retrospective study using a multi-institutional electronic medical records database in Taiwan. We included advanced NSCLC patients newly receiving osimertinib as second-line or beyond systemic therapy between January 2020 and December 2020. The clinical outcomes were median progression-free survival (PFS) based on the Response Evaluation Criteria in Solid Tumors (RECIST), overall survival (OS). We applied Kaplan-Meier methods to estimate median PFS and OS. Uni-variable and multi-variable Cox regression models were applied to identify the prognostic factors.

Results We included 286 osimertinib naive users with a median age of 66.8 (IQR: 58.8–73.1) years, of whom 61.5% were female and 99.7% were stage 4. The median PFS and OS were 12.0 months and non-reach, respectively. Moreover, ECOG performance (HR: 1.82, 95% CI: 1.06–3.13), exon 19 deletion (HR: 0.57, 95% CI: 0.41–0.80), and liver metastasis (HR: 1.88, 1.24 – 2.85) were significantly related to PFS in the multi-variable analysis. In addition, we analysed the patients with ∆CT value of EGFR mutation. We found that the patients with higher value of ∆CT between T790M and L858R mutation had significantly worse OS (HR: 1.46, 95% CI: 1.08–1.96) and PFS (HR: 1.47, 95% CI: 1.15–1.81).

Conclusion and Relevance Osimertinib was an effective treatment option for advanced NSCLC patients in real-world experience. Tumour burden liver metastasis, ECOG performance and a mutation in exon 19 deletion were independent predictive factors for progression-free survival. Moreover, ∆CT between T790M and L858R mutation was also a predictive factor while using osimertinib. Future real-world studies with large sample size are suggested to confirm our findings.

Conflict of Interest No conflict of interest.