The occurrence of cholangiocarcinoma is due to changes that take place in the cells of the bile duct in the liver DNA—the material which gives guidance to our body related to all chemical process. The changes in instruction are caused by DNA mutation, due to which the cells start growing uncontrollably and finally form cancer.
The problems arising in the bile duct, which may or may not be due to the manifestation of cancer, such as irritation, inflammation, or any obstruction, cause dilemma in the digestive system or jaundice or lead to chronic diseases and produce parasitic infections.
The definitive cause of cholangiocarcinoma is still unknown. There are, however, cancer suppressor genes, which ultimately cause death of the cells and block cell division. Due to the mutations of DNA, cancer may occur as a result of turning on of oncogenes and turning off of the cancer suppressor genes.
For a cell to turn cancerous there is a need for changes in various genes. In some cancers, the risk factors are increased due to change in DNA by parents. However, most of the bile duct cancers are not caused by inherited gene changes.
Other expected causes of bile duct cancer are:
- Initial sclerosing cholangitis: It is a rare form of disease caused in the liver. It causes inflammation of the liver for a long period.
- Biliary stones: They are hard stones, which are similar to gallstones that appear in the bile duct, but look smaller.
- Infections: The liver fluke infection is caused by eating raw fish. Here, the infection is due to tiny parasitic worms known as liver flukes. Some of the parasites may stay longer in the bile duct and result in the formation of cancer. This problem is mostly found in Asian countries.
- Choledochal cysts: Any changes in the bile-filled sacs over the lining of the cells where the bile duct is connected can result in the formation of these cysts.
- Cirrhosis: Hepatitis and alcohol may damage the liver and produce a mark on the skin during the formation of cancer. It increases the risk of cholangiocarcinoma.
- Reflux: Flowing back of digestive juice from pancreas to the bile duct, which results in the inability to perfectly empty it, may cause cancer.
- Abnormalities in the duct: The presence of fluid-filled sacs or cysts in the bile duct from birth can result in cancer.
Other factors such as erythrogenic intestine cancer, diabetes, and virus hepatitis are also thought to cause this type of cancer, but further studies are needed to confirm their exact role.
The factors that increase the risk of cancer are termed as risk factors. Different diseases will have different risk factors. It does not mean that having one or more risk factor will lead to cancer.
As the causes of this cancer still remain unidentified, researchers think that a few risk factors play a vital role in triggering it.
The risk factors include:
- Gallstones: Gallstones get struck and remain in the bile duct for a long period of time, obstructing its proper functioning.
- Physique of a person: Overweight and obesity lead to the risk of growth of few cancers.
- Age: Bile duct cancer is generally not found in young people and children. More than 60 percent of cholangiocarcinoma-affected people are in the age group of 65 years and above.
- History of family genetics: Even though there is no evidence of inheritance of the disease, family history is thought to have some role in developing the cancer.
- Style of living
- Smoking: Owing to the use of tobacco, the risk of growth of bile duct tumor is increased.
- Exposure to dangerous chemicals: If proper protection is not provided to people working in chemical factories, it can increase the chance of getting affected by the disease. Chemicals such as asbestos, dioxins, radon, polychlorinated biphenyls, thorium dioxide, and nitrosamines are considered dangerous.
- Excess use of alcohol: The habit of drinking alcohol leads to bile duct cancer. It also escalates the risk of liver cancer.
- Ulcerative colitis: It affects the inner lining of the intestine, which causes damage to it. Studies indicate that people with ulcerative colitis seem to have moderate risk of expanding bile duct cancer; about 1 in 200 people with ulcerative colitis is expected to have the risk.
In nearly 1 out of 10 people with ulcerative colitis, the complete intestine is infected and consists of primary sclerosing cholangitis.
At present, the specialists are thinking that the risk factor associated with bile duct cancer is PSC rather than ulcerative colitis.
Reviewed by Afsaneh Khetrapal BSc (Hons)