['The sensitivity and reliability of the biomarkers thymidine kinase 1 (TK1) and Ki-67 were studied in relation to clinical features and prognosis of survival for pathological-T1 (pT1) lung adenocarcinoma patients.', 'TK1 and Ki-67 expression was determined in 80 patients with pT1 adenocarcinoma of the lung and in 20 specimens from normal lung tissues, using immunohistochemistry.', 'TK1 was found in most lung tumor cells both in the cytoplasm and the nuclei. The positive labelling index (LI) for total TK1 was significantly higher than that for Ki-67. There was a significant correlation between the LI of total TK1 and lymph node metastasis, degree of tumor invasion and pathologic stages, which was not found for Ki-67. In addition, the overall 5-year survival of patients was statistically significant different between low and high levels of TK1 expression, but not in cases of Ki-67. A multivariate analysis revealed that expression of TK1, lymph node involvement and TNM pathology staging could serve as independent prognostic factors for the disease progression of pT1 lung adenocarcinoma patients.'] Is thymidine kinase 1 a better prognostic marker than Ki-67 for pT1 adenocarcinoma of the lung?