Background and purpose: The EGFR, K-ras, EML4–ALK, and BRAF genes are oncogenic drivers of lung adenocarcinoma. We conducted this study to analyze the mutations of these genes in stage I adenocarcinoma. Methods: The subjects of this retrospective study were 256 patients with resected stage I lung adenocarcinoma. We analyzed mutations of the EGFR, K-ras, and BRAF genes, and the EML4–ALK fusion gene. We also assessed disease-free survival (DFS) to evaluate the prognostic value and overall survival (OS) to evaluate the predictive value of treatment after recurrence. Results: Mutations of the EGFR, K-ras, EML4–ALK, and BRAF genes were detected in 120 (46.8 %), 14 (5.5 %), 6 (2.3 %), and 2 (0.8 %) of the 256 tumors. Two tumors had double mutations (0.8 %). The incidence of EGFR mutations was significantly higher in women than in men. The EML4–ALK fusion gene was detected only in younger patients. The DFS and OS of the K-ras mutant group were significantly worse than those of the EGFR mutant group, the EML4–ALK fusion gene group, and the wild-type group. Six of the seven patients with the EML4–ALK fusion gene are still alive without recurrent disease. Conclusions: In patients with stage I adenocarcinoma, mutation of the K-ras gene was a poor prognostic factor for recurrence. The presence of a mutation of the EGFR or EML4–ALK gene was not a prognostic factor.
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