E-Cadherin and vimentin protein expression was assessed in late stage non-small cell lung cancer tumors from the placebo controlled clinical trial, NCIC-CTG BR.21, to determine if these markers had the potential to predict outcome of erlotinib therapy. E-Cadherin and vimentin protein expression levels were assessed in tumors from 95 patients, who were representative of the overall population, using semi-quantitative immunohistochemistry. The percentage of tumor cells with grades 0, 1, 2, or 3 membrane staining of E-cadherin and cytoplasmic staining of vimentin was measured. Three scoring methods and multiple cut-offs were explored to determine if these markers were able to divide patients into groups with different overall survival (OS). A cut-off point for E-cadherin of ≥40% tumor cells with staining of +2 and +3 and a cut-off for vimentin of ≥10% of tumors cell with any staining provided the optimal stratification. The OS hazard ratio (HR) for E-cadherin(+) versus E-cadherin(-) in the erlotinib-treated patients was 0.68 (0.35-1.33) compared with 1.48 (0.69-3.15) in the placebo patients and the OS (HR) for erlotinib versus placebo was 0.47 (0.26-0.88) in E-cadherin(+) patients compared with 1.12 (0.52-2.44) in the E-cadherin(-) patients. The OS (HR) for vimentin(+) versus vimentin(-) in the erlotinib-treated patients was 0.65 (0.31-1.38) compared to 2.32 (1.09-4.94) in the placebo-treated patients and the OS (HR) for erlotinib versus placebo was 0.26 (0.11-0.63) in vimentin(+) compared to 0.99 (0.55-1.76) in the vimentin(-) patients. Similar trends were observed for progression-free survival and response rate. E-Cadherin and vimentin are biomarkers worthy of additional study as predictive markers of outcome of erlotinib therapy.