Abstract: To explore the role of protein expression of DNA methyltransferase 1 (DNMT1) in lung adenocarcinoma carcinogenesis and prognosis. MethodsDNMT1 protein expression levels in 95 tumor specimens and adjacent normal tissues were determined by immunohistochemistry. Comparisons of the survival rate and recurrence between positive and negative DNMT1 were conducted with SPSS13.0 software. ResultsNone of the 95 noncancerous tissues exhibited DNMT1 immunoreactivity, whereas 48 (50.5%) of the 95 lung adenocarcinoma cancerous tissues were DNMT1positive. There was a significant correlation between DNMT1 overexpression and gender (P=0.018), which was much more obvious in females. No correlation was found between DNMT1 expression and patient age, smoking, lymph node metastasis, tumor types and clinical stages (P＞0.05). In addition, general survival rate， 2year survival rate and diseasefree rate in patients with DNMT1positive were 31.91%, 65.07% and 48.65% respectively, while in patients with DNMT1negative they were 62.88%，　83.01% and 26.85%. DNMT1 protein overexpression served as a marker of poor prognosis by KaplanMeier and LogRank analysis(P＜0.05). ConclusionDNMT1 overexpression is an early event of lung adenocarcinoma carcinogenesis and plays a significant role in the development of lung adenocarcinoma. It may serve as a molecule marker to detect lung adenocacinoma in an early stage and an indicator of unfavourable prognosis.

Key words: DNA methylation, Lung neoplasms, Prognosis