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Background and objective The present study aims to detect the expressions of the thyroid transcription factor 1 (TTF-1) mRNA and protein in Xuanwei lung adenocarcinoma line (XWLC-05). We also investigated the relationship of TTF-1 with Ki-67 protein and analyzed the prognostic value of the TTF-1 protein in Xuanwei lung adenocarcinoma patients. Methods The expression of TTF-1 mRNA was evaluated by quantitative real-time RT-PCR (qRT-PCR), while proteins of TTF-1 and Ki-67 were detected by immunohistochemistry in XWLC-05. The expressions of TTF-1 and Ki-67 was detected in 96 resected cases of Xuanwei lung adenocarcinoma by immunohistochemistry from January 2008 to March 2012. Results TTF-1 mRNA was low and protein was absent in XWLC-05. The expression of Ki67 protein was 100% (high proliferative activity) in XWLC-05. All samples were Xuanwei lung adenocarcinoma (n=96) and TNM stages were I-II 66% (63/96) and III 34% (33/96). Immunohistochemical analysis showed the expression of TTF-1 in 89 (93%) of 96 and Ki-67 in 69 (70%) of 96. The positive rate of TTF-1 protein was 38 (96%) of 39 in well-differentiated phenotype and 51 (89%) 57 in moderately/poorly-differentiated phenotype. Patients with strong immunohistochemical expression of TTF-1 were statistically associated with well-differentiated phenotype (P=0.002), has inverse correlation with Ki-67 expression (P=0.01), and no correlation with age, sex, smoking history, and stages. The result from the Kaplan-Meier survival analysis showed that stages TTF-1 and Ki-67 were significantly associated with the prognosis of Xuanwei lung adenocarcinoma patients. The median progression-free survival in patients with I-II stages, strong positive expression TTF-1 and negative, and weak expressions Ki-67 groups was remarkably higher than those patients with III stage (46 months vs 32 months, P=0.001), negative and weak expressions TTF-1 (45 months vs 35 months, P=0.036) and strong positive expression Ki-67 groups (46 months vs 40 months, P=0.048), respectively. Conclusion Our results presented here suggest that TTF-1 may serve as a tumor suppressor gene based on its inverse correlation with Ki-67 proliferative activity. Patients with strong TTF-1 protein expression group tend to have a significantly better prognosis than patients with negative and weak TTF-1 protein expression group in Xuanwei lung adenocarcinoma.