Background: In the ADAURA study, patients with stage IB-IIIA of resected EGFR mutated lung adenocarcinoma receiving adjuvant osimertinib had a 2-year survival of 89% versus 52% in the placebo group (p<0.001), however, predictive markers of response and recurrence are still needed. Circular RNA (circRNA) is a type of RNA which forms a covalently closed continuous loop. Some circRNAs have been reported as essential for tumor cell proliferation through functions distinct from the canonical linear RNA. In this project, we studied circRNA expression levels in formalin-fixed paraffin-embedded (FFPE) lung tumor samples in order to explore potential biomarkers that could predict the benefit of adjuvant EGFR TKIs in EGFR-mutant NSCLC patients. Methods: FFPE tumor samples from patients with EGFR-mutant, stage I-IIIB NSCLC (n=79) were collected. RNA was purified using the High Pure FFPET RNA Isolation Kit (Qiagen) and quantified by Nanodrop 2000 (Thermo Scientific). A total of 250 ng of RNA were subjected to overnight hybridization and downstream nCounter processing (NanoString) following manufacturer’s instructions for our circRNA custom panel. Differential expression analysis was performed using Excel (Microsoft) and Prism GraphPad (Dotmatics) software. Results: Analysis of the 79 samples included in the study shown a cluster of 3 circRNAs significantly upregulated (p<0.05 and >2 fold-change) in EGFR mutation-positive NSCLC relapsing withing the 36 months after resection, including circRUNX1, circFUT8 and circAASDH. Disease-free survival (DFS) was significantly shorter for the subgroup of patients with high versus low circRUNX1 expression. Additional multivariate analysis identified circRUNX1 expression and tumor stage as the only statically significant prognostic factors (circRUNX1 hazard ratio = 4.480, confidence interval = 2.172-9.239, P < 0.001; pathological stage hazard ratio = 2.237, confidence interval = 1.183- 4.231, P = 0.008). Conclusions: CircRUNX1 could be a novel biomarker to predict the benefit of adjuvant EGFR TKIs with regards to DFS in EGFR-mutant resected NSCLC patients.