Moreover, recent studies have suggested that many esophageal squamous cell carcinoma cells express mu-opioid receptors, which may promote tumor cell growth and facilitate metastasis [16] This has raised concerns that opioid use in the postoperative period after esophageal cancer surgery may have adverse effects on long-term oncologic outcomes, such as OS or RFS. This evidence concerns the gene OPRM1 and esophageal squamous cell carcinoma.