Bile duct cancer - Causes of bile duct cancer

The exact cause of bile duct cancer is unknown, although some things can increase the risk of developing the condition.

Cancer begins with a change (mutation) in the structure of the DNA in cells, which can affect how they grow. This means that cells grow and reproduce uncontrollably, producing a lump of tissue called a tumour.

If left untreated, cancer can grow and spread to other parts of your body, either directly or through the blood and lymphatic system.

Increased risk

A number of factors that increase the risk of developing bile duct cancer have been identified. Some of these are discussed below.

Age

Your chances of developing cancer of the bile duct increase as you get older. Most people with the condition are over 65 years old.

Primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a rare type of liver disease that causes long-lasting (chronic) inflammation of the liver.

It usually occurs in people aged 30-50. Up to 10% of people with ulcerative colitis (inflammation of the colon and rectum) also have PSC.

Around 10-20% of people with PSC will develop bile duct cancer. Your risk of developing bile duct cancer is thought to be higher if you have PSC and you smoke.

Bile duct abnormalities

Some people can have fluid-filled sacs (cysts) in their bile duct. These cysts are usually congenital, which means they are present from birth.

The most common types are choledochal cysts and Caroli's disease, but both conditions are very rare.

Up to 20% of people with choledochal cysts that are not removed will develop cancer of the bile duct.

Biliary stones

Biliary stones are similar to gallstones, except they form inside the liver rather than inside the gallbladder.

Biliary stones are rare in western Europe, but are relatively common in parts of Asia, such as Japan and Taiwan. It is estimated that approximately 10% of people with biliary stones will develop bile duct cancer.

Parasitic infection

Liver flukes are a type of parasitic insect known to increase the risk of developing bile duct cancer. You can become infected with liver flukes by eating undercooked fish that has been contaminated with fluke eggs.

Liver fluke infections are usually only a problem in Asia (especially Thailand) and Africa, where liver flukes are more widespread.

Exposure to toxins

Exposure to certain chemical toxins is known to increase the risk of developing bile duct cancer.

For example, if you are exposed to a chemical called thorotrast, your chances of developing bile duct cancer rises. Thorotrast was widely used in radiography until it was banned during the 1960s after its dangerous properties were fully understood.

Other toxins that may increase your chances of developing cancer of the bile duct include:

• asbestos – a fire-resistant material that was widely used in construction and manufacturing, but is now banned in this country
• polychlorinated biphenyls (PCBs) – a chemical that was used in manufacturing and building but, like asbestos, has now been banned

Other factors

The following factors are linked with an increased risk of developing bile duct cancer, but more research is still needed:

• hepatitis B and hepatitis C
• cirrhosis (a scarred liver) as a result of drinking excess amounts of alcohol
• HIV
• diabetes
• obesity
• smoking