Epidermal growth factor receptor tyrosine kinase inhibitors for de novo T790M mutation: A retrospective study of 44 patients

BACKGROUND: This study aimed to evaluate possible treatment strategies for patients with de novo T790M mutation‐positive (T790M+) non‐small‐cell lung cancer (NSCLC). METHODS: Patients diagnosed with de novo T790M+ NSCLC and treated with epidermal growth factor receptor tyrosine kinase inhibitors (EGFR‐TKIs) between 2011 and 2018 at a regional hospital in Taiwan were retrospectively reviewed. Their clinicopathological characteristics and subsequent treatment information were collected, and potential prognostic factors were identified using univariate and multivariate analyses. RESULTS: All tumors with T790M mutations coexisted with sensitizing mutations. Through the last follow‐up in May 2021, afatinib and osimertinib demonstrated better progression‐free survival (PFS, p < 0.01) and overall survival (OS, p < 0.01) than gefitinib and erlotinib. Additionally, patients with low T790M ratios had better PFS than those with high T790M ratios, implying that the proportion of T790M+ tumors determined the response to EGFR‐TKIs. Multivariate analysis confirmed that both EGFR‐TKI treatment (osimertinib hazard ratio [HR] 0.06, 95% confidence interval [CI] 0.01–0.30; afatinib HR 0.09, 95% CI 0.02–0.39) and a low T790M ratio (HR 0.29, 95% CI 0.12–0.69) were independently favorable prognostic factors for patients with de novo T790M+ NSCLC. Median PFS was 6.1 (95% CI 4.4–7.8) months. In addition, patients treated with first‐generation (1G)/second‐generation (2G) EGFR‐TKIs followed by osimertinib (n = 8) demonstrated the best OS compared with patients treated with frontline osimertinib (n = 5) or 1G/2G EGFR‐TKIs without osimertinib (n = 28, p < 0.01). CONCLUSION: Sequential TKIs may represent an alternative option for de novo T790M mutation, particularly frontline afatinib and tumors with low T790M ratios.