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), which is found in all human cells.
A change in the code is known as a mutation, and it 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 that is 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, pancreas or 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) that are located throughout your body, much like your blood circulation system. The glands produce many of the specialised cells that are needed by the immune system (the body’s natural defence against infection and illness).
Risk factors
It is unclear exactly what causes the cells in the bile duct to turn cancerous. However, a number of risk factors have been identified that make it more likely that you will develop the condition. These are discussed below.
Primary sclerosing cholangitis
Primary sclerosing cholangitis (PSC) is a rare type of liver disease that causes chronic (long-lasting) inflammation of the liver.
PSC affects about 1 in 16,000 people, and usually occurs in people who are 30-50 years old. An estimated 10-20% of people with PSC will go on to develop bile duct cancer.
Your risk of developing bile duct cancer is thought to be higher if you have PSC and you smoke tobacco.
Viral hepatitis
Hepatitis B and hepatitis C are two types of viral liver infection that are thought to cause a 10-fold increase in the risk of a person developing bile duct cancer.
Studies have found that about 1 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 such circumstances, the risk of developing bile duct cancer is thought to be a thousand times higher compared to that of the general population.
Parasitic infection
Liver flukes are a type of parasitic insect that are 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.
Billiary stones
Billiary stones are similar to gallstones except that they form inside the liver rather than inside the gallbladder.
Billiary stones are rare in western Europe, but they are relatively common in parts of Asia, such as Japan and Taiwan. It is estimated that approximately 10% of people with billiary stones will develop bile duct cancer.
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 has now been banned in this country
- polychlorinated biphenyls (PCBs) – a chemical that was used in manufacturing and building but, like asbestos, has now been banned
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:
People who have either one of these conditions are four times more likely to develop bile duct cancer than the population at large. However, this increased risk is still very small. It is estimated that a person with an inflammatory bowel disease only has a 1 in 1,500 chance of developing bile duct cancer.
