Considering the potential hormonal role in biliary tract cancers, genetic variants in ESR1 and ESR2 genes have revealed an association between ESR polymorphism [ESR1 rs1801132 (P325P)] and bile duct cancer, which was more pronounced among patients with a low BMI or without biliary stones through their effect on estrogenic activity [36–37]. The gene discussed is ESR1; the disease is bile duct cancer.