In this study, we comprehensively performed an in-depth analysis on AQP9 expression and its impact on prognosis in different cancers, and we also probed the association of AQP9 expression with tumor immune cell infiltrating levels in breast invasive carcinoma (BRCA), colon adenocarcinoma (COAD), lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC) and stomach adenocarcinoma (STAD). This evidence concerns the gene AQP9 and lung adenocarcinoma.