| Summary: | Background: Epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) are standard treatments for advanced EGFR-mutated non–small cell lung cancer (NSCLC) patients. Osimertinib is an effective therapy for NSCLC patients with acquired resistance due to T790M mutation after first- and second-generation EGFR-TKI treatment. This study aimed to analyze the clinical outcomes of sequential therapy following first-line EGFR-TKIs and the predictive factors of an acquired T790M mutation. Methods: Between January 2014 and December 2018, data from 2190 advanced NSCLC patients with common EGFR mutations (exon 19 deletion and L858R) receiving first- and second-generation EGFR-TKIs in Linkou, Kaohsiung, Chiayi and Keelung Chang Gung Memorial Hospitals were retrospectively retrieved and analyzed. Results: Until August 2021, among 1943 patients who experienced progressive disease, 526 underwent T790M mutation tests, and their T790M-positive rate was 53.6%. Exon 19 deletion mutation and progression-free survival (PFS) of >12 months were positively associated with secondary T790M mutation. Different first-line first- and second-generation EGFR-TKI therapies did not affect the appearance of acquired T790M mutations. The median overall survival (OS) was 58.3 [95% confidence interval (CI): 49.0–67.5] months among the patients with T790M mutation who received second-line osimertinib therapy compared with 31.0 (95% CI: 27.5–34.5) months among the patients without T790M mutation who received chemotherapy alone. The multivariate analysis showed that a poor performance status (score: >2), nonadenocarcinoma histology, stage IV cancer, liver metastasis, brain metastasis, PFS while on first-line EGFR-TKIs, and subsequent chemotherapy without third-generation EGFR-TKIs were significant independent unfavorable prognostic factors for OS. Conclusion: This study demonstrated the efficacy of first-line EGFR-TKIs and sequential osimertinib therapy. The results of our study suggest that T790M mutation tests are important for the use of subsequent osimertinib, which yielded favorable survival outcomes.
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