ABSTRACT. This study aimed to detect micrometastatic tumor cells in the lymph nodes of patients with pN 0 lung adenocarcinoma using a combination of thyroid transcription factor-1 (TTF-1) expression and cytokeratin 7 (CK7) expression and to investigate the association of lymph node micrometastasis with the clinicopathological characteristics of patients with lung adenocarcinoma. A total of 54 patients with pN 0 lung adenocarcinoma and whose primary tumors were positive for both TTF-1 and CK7 expression were included in this study. In total, 893 lymph nodes were obtained from these 54 patients and were analyzed for micrometastasis by immunohistochemical staining with anti-CK7 and anti-TTF-1 antibodies. CK7-and TTF-1-positive cells were found in the lymph nodes of 9 (16.7%) of 54 patients, and 21 (2.4%) of 893 lymph nodes exhibited positivity for these factors. No cells positive for both CK7 and TTF-1 were detected in the 5 lymph nodes obtained from patients with benign lung tumors. Lymph node micrometastasis was found to be associated with the differentiation grade and primary tumor position (P < 0.05). The detection of lymph node micrometastasis by a combination of CK7 and TTF-1 immunohistochemical staining 5595 ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 13 (3): 5594-5600 (2014) Lymph node micrometastasis provides a more accurate assessment of tumor staging for pN 0 lung adenocarcinoma.