Objective:ASCL-1 gene expression is closely related to pulmonary neuroendocrine (NE) tumors, such as small cell carcino-ma, atypical carcinoid, carcinoid, and large cell NE carcinoma. This study aimed to analyze ASCL-1 protein expression in lung adenocar-cinoma (AD) and its correlation with prognosis. Methods:ASCL-1 protein expression in 283 cases of AD was determined through immu-nohistochemical analysis and compared with the expression of traditional NE markers, including chromogranin A, CD56, and synapto-physin. Western blot was performed to detect the ASCL-1 protein expression levels in AD. Single factor Chi-square test and Logistic multiple factor regression analysis were conducted to explore the factors related to ASCL-1 expression. Kaplan-Meier survival analysis was applied to evaluate the prognosis of patients with AD. Results:Immunohistochemical analysis showed that ASCL-1 expression was positive in 48/283 (16.9%) AD and positively correlated with NE markers (0