EGFR and squamous cell carcinoma: In the univariate analysis of DFS, age (≤60 vs. >60 years), smoking, pathological type (adenocarcinoma vs. squamous cell carcinoma), EGFR mutations status (exon 19 deletion vs. exon 21 L858R), different durations of EGFR-TKI therapy, and chemotherapy prior to the adjuvant EGFR-TKI therapy were not associated with DFS.