['This study was aimed at understanding the effect of β-catenin and cyclin D1 on overall survival in patients with early-stage NSCLC and at evaluating if the\xa0prognostic effect can be modified by adjuvant chemotherapy.', 'We retrospectively analyzed the expression of β-catenin and cyclin D1 using immunohistochemistry in formalin-fixed paraffin-embedded tissues from 576 patients with early-stage NSCLC.', 'The median duration of follow-up was 5.1 years. Overexpression of β-catenin and cyclin D1 was found in 56% and 50% of 576 cases, respectively. Overexpression of β-catenin and cyclin D1 was significantly associated with poor overall survival (p\xa0= 0.003 and p\xa0= 0.0009, respectively; log rank test) in squamous cell carcinomas, not in adenocarcinomas. The prognostic significance of each protein in the squamous cell carcinomas was limited to stages IA, IB, and IIA. In addition, simultaneous overexpression of β-catenin and cyclin D1 in the squamous cell carcinomas synergistically increased hazard ratios (HRs) 15.79 (95% confidence interval [CI]\xa0= 1.09-51.23; p\xa0=0.04) for stage IA, 10.30 (95% CI\xa0= 2.29-46.41; p\xa0= 0.002) for stage 1B, and 3.55 (95% CI\xa0= 1.22-10.36; p\xa0= 0.02) times for stage 2A compared to those without overexpression of the two proteins, after adjusting for confounding factors. In addition, the effect was not dependent on adjuvant chemotherapy.'] Is overexpression of β-Catenin and Cyclin D1 Associated with Poor Overall Survival in Patients with Stage IA-IIA Squamous Cell Lung Cancer Irrespective of Adjuvant Chemotherapy?