Cholangiocarcinomas (CCCs) are malignancies of the biliary duct system that may originate in the liver and extrahepatic bile ducts, which terminate at the ampulla of Vater. [1, 2, 3, 4] CCCs are encountered in three anatomic regions: intrahepatic, extrahepatic (ie, perihilar), and distal extrahepatic.
Perihilar tumors are the most common CCCs, and intrahepatic tumors are the least common. Perihilar tumors, also called Klatskin tumors (after Klatskin's description of them in 1965  ), occur at the bifurcation of right and left hepatic ducts.  Distal extrahepatic tumors are located from the upper border of the pancreas to the ampulla. More than 95% of these tumors are ductal adenocarcinomas; many patients present with unresectable or metastatic disease.
Cholangiocarcinoma is a tumor that arises from the intrahepatic or extrahepatic biliary epithelium. More than 90% are adenocarcinomas, and the remainder are squamous cell tumors. The etiology of most bile duct cancers remains undetermined. Long-standing inflammation, as with primary sclerosing cholangitis (PSC) or chronic parasitic infection, has been suggested to play a role by inducing hyperplasia, cellular proliferation, and, ultimately, malignant transformation. Intrahepatic cholangiocarcinoma may be associated with chronic ulcerative colitis and chronic cholecystitis.
Cholangiocarcinomas tend to grow slowly and to infiltrate the walls of the ducts, dissecting along tissue planes. Local extension occurs into the liver, porta hepatis, and regional lymph nodes of the celiac and pancreaticoduodenal chains. Life-threatening infection (cholangitis) may occur that requires immediate antibiotic intervention and aggressive biliary drainage.
Each year, approximately 2500 cases of cholangiocarcinoma occur, compared with 5000 cases of gallbladder cancer and 15,000 cases of hepatocellular cancer. The average incidence is one case per 100,000 population per year.
A study by Singal et al found that the frequency of intrahepatic cholangiocarcinoma has increased over time and is most commonly noted in women older than 60 years. 
Incidence in most Western countries ranges from 2 to 6 cases per 100,000 people per year. The highest annual incidences are in Japan, at 5.5 cases per 100,000 people, and in Israel, at 7.3 cases per 100,000 people.
Occupational cholangiocarcinoma has been documented in workers at printing companies in Japan who had been exposed to high concentrations of chemical compounds, including 1,2-dichloropropane (1,2-DCP) and/or dichloromethane.  Heavy infestation by the liver flukes Clonorchis sinensis (endemic predominantly in Asian countries, including Korea, China, Taiwan, Vietnam, and far eastern Russia) and Opisthorchis viverrini (the Southeast Asian liver fluke) has been linked to the development of cholangiocarcinoma. 
Despite aggressive anticancer therapy and interventional supportive care (ie, wall stents or percutaneous biliary drainage), median survival rate is low, since most patients (90%) are not eligible for curative resection. The overall survival is approximately 6 months.
Native Americans have the highest annual incidence in North America, at 6.5 cases per 100,000 people. This rate is about 6 times higher than that in non–Native American populations. The high prevalence of cholangiocarcinoma in people of Asian descent is attributable to endemic chronic parasitic infestation.
The male-to-female ratio for cholangiocarcinoma is 1:2.5 in patients in their 60s and 70s and 1:15 in patients younger than 40 years. According to the American Cancer Society, the number of new cases of liver and intrahepatic bile duct cancer in 2016 is estimated to be 28,410 for men and 10,820 for women, with estimated mortality of 18,280 and 8,890, respectively. The estimated number of new cases of gallbladder and other biliary cancers (extrahepatic cholangiocarcinoma) are 5,270 for men and 6,150 for women, with estimated mortality rates of 1,630 and 2,080, respectively. 
Highest prevalence rate occurs in males and females in their 60s and 70s.
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