For specific mechanisms, we found that retinol metabolism reduces cholangiocarcinoma risk59, allograft rejection occurs in kidney renal clear cell carcinoma60, ovarian steroidogenesis inhibits liver hepatocellular carcinoma61, MSH and MLH1 gene alterations in mismatch repair increase the oesophageal carcinoma risk62, and lung adenocarcinoma63 influences renin–angiotensin system gene expression. The gene discussed is REN; the disease is cholangiocarcinoma.