By contrast, the prognostic significance of ERα in resected early-stage lung adenocarcinoma remained unknown since previous study cohorts were either composed of only a small number of patients or were a heterogeneous population with regards to pathologic TNM stage (including early-stage and advanced-stage) and histology (including adenocarcinoma and squamous cell carcinoma). This evidence concerns the gene ESR1 and squamous cell carcinoma.