Which of the following is NOT a high risk factor for cholangiocarcinoma?

Cholangiocarcinoma is a rare tumor arising from the biliary epithelium and may occur anywhere along the biliary tree. About two thirds are located at the hepatic duct bifurcation. Risk factors associated with cholangiocarcinoma include, Primary sclerosing cholangitis Choledochal cysts Ulcerative colitis Hepatolithiasis Biliary-enteric anastomosis Biliary tract infections with Clonorchis Chronic typhoid carriers Liver flukes Dietary nitrosamines Thorotrast Exposure to dioxin Ref: Oddsdottir M., Pham T.H., Hunter J.G. (2010). Chapter 32. Gallbladder and the Extrahepatic Biliary System. In F.C. Brunicardi, D.K. Andersen, T.R. Billiar, D.L. Dunn, J.G. Hunter, J.B. Matthews, R.E. Pollock (Eds), Schwaz's Principles of Surgery, 9e