Kaplan-Meier curves for RFS of the test cohort stratified by the IASLC grading system (A: the entire cohort and C: stage I cohort) and predominant pattern-based grading system (B: the entire cohort and D: stage I cohort). For the latter, grade 1 is composed of lepidic predominant tumors; grade 2 of acinar and papillary predominant tumors, and grade 3 of solid, micropapillary, and complex glandular predominant tumors. IASLC, International Association for the Study of Lung Cancer; RFS, recurrence-free survival.