In conclusion, our study demonstrates that nuclear ERα expression is an independent predictor of increased risk of recurrence in small (pT1aN0) stage I lung adenocarcinoma, especially in males, and correlates with unfavorable prognostic immune microenvironments (FoxP3+ regulatory T lymphocyte infiltration and tumoral IL-7R overexpression). The gene discussed is FOXP3; the disease is lung adenocarcinoma.