GHRL and colorectal cancer: Our MR analyses focusing on gastrointestinal cancer were motivated by several previous observational studies that reported inverse associations between the total circulating levels of ghrelin and the risk of gastrointestinal cancers, including esophageal squamous cell carcinoma (9, 10), esophageal adenocarcinoma (11), stomach cancer (10, 12, 13), and colorectal cancer (in the years approaching diagnosis only; ref. 14).