Different prognostic role of EGFR mutation according to the IASLC histological grade in patients with resected early-stage lung adenocarcinoma

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.