This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Liver, Subject name: Pathology
Which is risk factor for cholangiocarcinoma - 
Select and explain. 
A. Obesity, B. Primary sclerosing cholangitis, C. Salmonella carrier state, D. HBV infection
B: Primary sclerosing cholangitis
Answer: B: Primary sclerosing cholangitis 
Explanation: Ans. is 'b' i.e., Primary sclerosing choiangiocarcinoma Cholangiocarcinomao Cholangiocarcinoma is malignancy of the biliary tree, arising from bile ducts within or outside the liver,o Risk factors:Primary sclerosing cholangitisCongenital fibropolycystic disease of the biliary system (caroli disease, choledochal cyst).Exposure to thorotrast.Opisthorchis sinensis infection.Pathologyo Cholangiocarcinoma are adenocarcinoma arising from bile ducts epithelium,o Most are well to moderately differentiated.o Markdly desmoplastic, with dens collegenous stroma separating the glandular elements,o Cells are not bile stained, because bile is synthesized by hepatocytes and not by bile duct epithelium.