Causes of bile duct cancer

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

How cancer begins

Cancer begins with a change in the coding information in cells that tells them when to grow and replicate. The code is read from deoxyribonucleic acid (DNA), found in all human cells.

A change in the code is known as a mutation, and can alter the instructions that control cell growth. The mutation can instruct the cells to carry on growing instead of stopping when they should. This causes the cells to reproduce uncontrollably, resulting in a lump of tissue known as a tumour.

How cancer spreads

If left untreated, cancer can quickly grow and spread to other parts of your body.

There are two ways that bile duct cancer can spread:

• directly – the cancer spreads out of the bile duct and into surrounding tissue and organs, such as the liver and its blood vessels, the pancreas or the gallbladder
• indirectly – the cancer cells spread via the blood or lymphatic system (see below) to other parts of the body, such as the lungs and bowel

The lymphatic system is a series of glands (or nodes) located throughout your body, much like your blood circulation system. The glands produce many of the specialised cells needed by the immune system (the body’s natural defence against infection and illness).

Increased risk

A number of things have been identified that make it more likely that you will develop the condition. Some of these are discussed below.

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 who are between the ages of 30 and 50. In most cases, PSC is associated with chronic inflammation of the colon (ulcerative colitis).

It is not known exactly how many people with PSC will develop bile duct cancer, but estimates vary from 5-35%.

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.

It is estimated that 6-30% of people with these conditions 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.

Inflammatory bowel disease

Inflammatory bowel disease is a general term that describes a number of conditions that cause inflammation inside the digestive system. The two most common types (although still rare in general terms) of inflammatory bowel disease are:

• ulcerative colitis, which affects around 100,000 people in England
• Crohn’s disease, which affects around 90,000 people in England

People who have either of these conditions are four times more likely to develop bile duct cancer than the population at large. However, this increased risk is still small. It is estimated that a person with an inflammatory bowel disease only has a one in 1,500 chance of developing bile duct cancer.

Viral hepatitis

Hepatitis B and hepatitis C are two types of viral liver infection thought to cause a tenfold increase in the risk of a person developing bile duct cancer.

Studies have found that about one in 10 people who develop bile duct cancer test positive for a hepatitis B or hepatitis C infection.

The risk is increased further if a person with hepatitis C has cirrhosis (a scarred liver) as a result of drinking excess amounts of alcohol. In these circumstances, the risk of developing bile duct cancer is thought to be 1,000 times higher compared to that of the general population.

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 which 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

• age – your chances of developing cancer of the bile duct increase as you get older: most people with the condition are over 65 years of age
• non-alcholic fatty liver disease
• diabetes