Refined Stratification Based on Baseline Concomitant Mutations and Longitudinal Circulating Tumor DNA Monitoring in Advanced EGFR-Mutant Lung Adenocarcinoma Under Gefitinib Treatment

Abstract Introduction The optimal treatment for EGFR-mutant lung adenocarcinoma (LUAD) remains challenging because of intratumor heterogeneity. We aimed to explore a refined stratification model based on the integrated analysis of circulating tumor DNA (ctDNA) tracking. Methods ctDNA was prospectively collected at baseline and at every 8 weeks in patients with advanced treatment-naive EGFR-mutant LUAD under gefitinib treatment enrolled in a phase 2 trial and analyzed using next-generation sequencing of a 168-gene panel. Results Three subgroups categorized by baseline comutations—EGFR-sensitizing mutations (59, 32.8%), EGFR-sensitizing mutations with tumor suppressor mutations (97, 53.9%), and EGFR-sensitizing mutations with other driver mutations (24, 13.3%)—exhibited distinct progression-free survival (13.2 [11.3–15.2] versus 9.3 [7.6–10.5] versus 4.0 [2.4–9.3] months) and overall survival (32.0 [29.2–41.5] versus 21.7 [19.3–27.0] versus 15.5 [10.5–33.7] months, respectively), providing evidence for initial stratification. A total of 63.7% of the patients achieved week 8 ctDNA clearance, with significant difference noted among the three subgroups (74.5% versus 64.0% versus 29.4%, respectively, p = 0.004, Fisher’s exact test). Patients without week 8 ctDNA clearance had worse progression-free survival (clearance versus nonclearance 11.2 [9.9–13.2] versus 7.4 [5.6–9.6] months, p = 0.016, Cox regression], especially in the second subgroup [5.8 (5.6–11.5) months], suggesting the necessity of adaptive stratification during treatment. During follow-up, 56.0% and 20.8% of the patients eventually harbored p.T790M and non-p.T790M mutations, respectively, with a significant difference in non-p.T790M mutations among the three subgroups (7.5% versus 15.7% versus 80.0%, respectively, p Conclusions The patients with baseline comutations and ctDNA nonclearance at first visit might require combined therapy because of the limited survival benefit of EGFR tyrosine kinase inhibitor monotherapy. We proposed a refined stratification mode for the whole-course management of EGFR-mutant LUAD.