Aims: The prognostic role of EGFR mutations remains controversial. We aimed to evaluate the prognostic role of EGFR mutation in consideration of the IASLC histological grade in patients with resected early-stage lung adenocarcinoma.

Methods and results: A total of 3297 patients with stages I-IIA resected lung adenocarcinoma who had had EGFR mutation tests between January 2014 and December 2019 at the Samsung Medical Center, Seoul, Korea were included. Recurrence-free survival (RFS) was compared by EGFR mutation status (EGFR-M+ versus EGFR-WT) and IASLC histological grade (G1, G2 and G3). Cox proportional hazards models were used to estimate the adjusted HRs (aHRs) and 95% confidence intervals (CIs).

Results: Compared to the EGFR-WT group, the EGFR-M+ group had a significantly lower proportion of G3 tumour (16 versus 33%, P < 0.001). During a median follow-up of 41.4 months, 376 patients experienced recurrence. After adjusting for histological grade, the aHR for recurrence comparing the EGFR-M+ to the EGFR-WT was 1.30 (95% CI = 1.04-1.62, P = 0.022). The EGFR-M+ group had a significantly lower 5-year RFS than the EGFR-WT group among G3 patients (58.4 versus 71.5%, P < 0.001), but not among G1 and G2 patients.

Conclusions: EGFR mutation status was associated with a risk of recurrence after consideration of the IASLC histological grading, especially in G3 tumours. The results of this study would be useful for developing a new staging system and identifying a subset of patients who may benefit from adjuvant targeted therapy.