ABSTRACT
<p><b>BACKGROUND</b>Yes-associated protein (YAP) plays an important role in signal transduction and gene transcription regulation in normal cells, with elevated and over-expressed YAP levels observed in various malignant tumors. The aim of this study was to investigate the expression of YAP in non-small cell lung cancer (NSCLC), and to study the possible relationship of YAP expression with the occurrence and development of NSCLC.</p><p><b>METHODS</b>YAP expression was assessed in 40 cases of NSCLC tumor tissues by immunohistochemistry, and their protein and mRNA levels were evaluated through Western blotting and reverse transcription-polymerase chain reaction (PCR), respectively. Normal lung tissues obtained from the same patient were used as control. Statistical analysis was performed to correlate the YAP expression to clinical pathological factors, such as tumor type, stage and grade.</p><p><b>RESULTS</b>YAP-positive expression was found in 28 (70%) of the 40 cases of NSCLC, which included 10 cases of squamous cell carcinoma (25%), 17 cases of adenocarcinoma (42.5%) and 1 case of squamous adenocarcinoma (2.5%). In the 28 YAP-positive cases, 19 cases showed lymph node metastasis and were classified in TNM stage II + III (47.5%); the other nine cases showed no lymph node metastasis (22.5%) and were classified in the TNM stage I. There was no relationship between YAP expression and patients' age, gender or tumor histological grades. However, YAP showed significant over expression in late period of T stage (P = 0.012), TNM stage (P = 0.039), and lymph node metastasis (P = 0.013), respectively. Notably, YAP-positive expression was significantly higher in adenocarcinoma than that in squamous cell carcinoma (P = 0.041).</p><p><b>CONCLUSIONS</b>Over-expression of YAP was associated with NSCLC, especially lung adenocarcinoma. The high YAP expression in late period of tumor stage and lymph node metastasis may indicate that YAP expression could be an early marker for NSCLC tumorigenesis.</p>