2.2. Survival analysis

We introduced four online databases to perform the survival analysis for the ACE2 gene in COAD. We first evaluated the impact of ACE2 expression on the overall survival (OS) outcome of COAD patients, using the OncoLnc database (http://www.oncolnc.org/) ^[41], and the meta-survival analysis option in the Gene Expression database of Normal and Tumor tissues 2 (GENT2) database (http://gent2.appex.kr/gent2/) ^[42]. Then, we utilized the LOGpc database (http://bioinfo.henu.edu.cn/DatabaseList.jsp) to assess the impact of ACE2 expression and several clinical features of COAD patients, including TNM staging, sex, lymph node, and race on their OS outcome. In addition, we used “Gene_Outcome module” from Tumor Immune Estimation Resource2.0 (TIMER2.0) web tool (http://timer.cistrome.org/) ^[43] to investigate the relevance of ACE2 gene expression and clinicopathological characteristics of COAD patients (age, gender, race, and stage) with OS outcome. To conduct these analyses, a p-value < 0.05 was set as a cut-off, and COAD patients were divided into high expression and low expression groups based on the median of ACE2 expression levels in their tumor tissues.