['The purpose of this study is to clarify the correlations between the expression of membrane-bound estrogen receptor-α (mERα) and epidermal growth factor receptor (EGFR) mutation and clinicopathological factors, especially in relation to the prognosis, in patients with lung adenocarcinoma.', 'We conducted a retrospective review of the data of 51 lung adenocarcinoma patients with tumors measuring less than 3\u2009cm in diameter. Immunohistochemical staining for mERα expression and detection of the EGFR mutation status were performed.', 'Among the 51 patients, the tumors in 15 showed both mERα expression and EGFR mutation. ("double positive") Significant associations between "double positive" and vascular invasion, vascular endothelial growth factor expression, and Ki-67 expression were observed. A multivariate analysis revealed that only "double positive" was an independent risk factor influencing the recurrence-free survival.'] Are membrane-bound estrogen receptor-α expression and epidermal growth factor receptor mutation associated with a poor prognosis in lung adenocarcinoma patients?