In general, cancer begins when a genetic mutation (change in certain genes) turns normal, healthy cells into abnormal cells. Healthy cells grow and multiply at a set rate and eventually die at a set time. Abnormal cells grow and multiply out of control, and they do not die. The abnormal cells clump together to create a mass (tumor). Cancer cells invade nearby tissues and can separate from an initial tumor to spread to other parts of the body (metastasize).
Certain chemicals, such as aflatoxins (harmful substances that are found in poorly stored grains and nuts), damage the DNA in liver cells. DNA contains genes that tell cells how to carry out their jobs. When DNA is damaged, it can no longer stop liver cells from growing too much. As a result, abnormal cells begin to grow more quickly and form tumors.
Infection with hepatitis viruses can also damage DNA. In the United States, hepatitis C infection causes about half of all cases of hepatocellular carcinoma, the most common type of liver cancer. Hepatitis C is spread by transfusions of blood that has not been properly screened, contaminated needles used to inject drugs or for tattooing or body piercing. Some researchers believe that the hepatitis C virus interferes with a gene that stops cells from reproducing too quickly. Hepatitis B virus can also cause liver cancer. This virus is spread through unprotected sex and contaminated needles. The virus inserts some of its genetic material into healthy liver cells, which stops the liver cells from functioning properly.
Drinking too much alcohol for a long period of time can cause a disease known as cirrhosis, a disease in which scar tissue replaces normal liver tissue, making it harder for the liver to carry out its functions. Patients with cirrhosis are at higher risk for liver cancer.
A small proportion of liver cancers are inherited mutations in a person’s genes. However, most of the genetic mutations that cause liver cancer are not inherited. Instead, these mutations are caused by exposure to substances in the environment or diet. Scientists have not yet identified the substances that cause the genetic mutations that lead to liver cancer.
Risk Factors for Liver Cancer
Doctors and researchers believe that certain factors, known as risk factors, increase a person’s chances of getting liver cancer. The more risk factors you have, the higher your chance of liver cancer. However, not everyone with a risk factor will develop liver cancer and people without any risk factors can develop the disease.
Risk factors for liver cancer include:
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Age - Liver cancer is much more common in people over age 60 than in younger people.
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Alcohol - Drinking too much alcohol (more than two drinks a day) for long periods of time can cause cirrhosis (see below). Cirrhosis caused by long-term (chronic) alcohol consumption is the most common risk factor for hepatocellular carcinoma in economically developed countries.
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Anabolic steroids - People who take anabolic steroids to build muscle and increase bone growth have an increased risk of hepatic adenomas. These are benign (noncancerous) liver tumors, but they can become cancerous.
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Chemicals in the environment - Certain chemicals can cause liver cancer. These chemicals include:
- Aflatoxins are harmful substances made by certain types of mold that are often found in grains and nuts stored in a moist environment. The U.S. Food and Drug Administration (FDA) does not allow food with high levels of aflatoxin to be sold in the United States.
- Vinyl chloride is a chemical used to make certain plastics, and thorium dioxide or Thorostat, a chemical that used to be injected into patients during certain x-ray tests. Thorostat is no longer used and the U.S. government limits worker exposure to vinyl chloride.
- Arsenic is a naturally occurring substance sometimes found in drinking water.
- Cirrhosis - With cirrhosis, scar tissue replaces normal liver tissue, making it harder for the liver to carry out its functions. In the United States, cirrhosis is usually caused by chronic alcohol consumption. But cirrhosis can also be caused by chronic infections with hepatitis B or C virus, certain drugs, and certain diseases (such as hemochromatosis—see inherited diseases below).
- Primary biliary cirrhosis is an inflammation of the bile ducts in the liver. People with primary biliary cirrhosis have a much higher risk of cholangiocarcinoma.
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Diabetes - People with diabetes, especially if they drink a lot of alcohol and/or have chronic hepatitis, have an increased risk of liver cancer.
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Family history - People with family members who have or have had liver cancer might have an increased risk of the disease.
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Gender - Hepatocellular carcinoma is about twice as common in men as women in the United States.
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Hepatitis - Long-term (chronic) infection with the hepatitis B or hepatitis C virus is the most common risk factor for liver cancer. These infections can cause cirrhosis of the liver. Infection with hepatitis C is more common in the United States, while hepatitis B infection is more common in Asian and economically developing countries. People infected with hepatitis B or C virus have a very high risk of developing chronic hepatitis, cirrhosis, and liver cancer. The hepatitis B and C viruses can be spread by exposure to someone else’s blood or body fluids as a result of injury, sharing needles to inject drugs, or sexual contact. Hepatitis B can also be spread from a pregnant woman to her unborn baby.
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Inherited diseases - Certain inherited diseases such as hemochromatosis can cause cirrhosis and thus liver cancer. People with hemochromatosis absorb too much iron from their food. The high levels of iron in their liver can cause cirrhosis. Several other rare inherited diseases can cause cirrhosis.
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Obesity - People who are obese have a higher risk of liver cancer.
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Oral contraceptives (birth control pills) - Some scientists believe that oral contraceptives can increase a woman’s risk of liver cancer. However, the studies that showed an increased risk tested a kind of birth control pill that is no longer used. Scientists do not know yet whether the birth control pills women take today can increase liver cancer risk.
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Tobacco - Some studies have found that smoking can increase liver cancer risk.
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Ulcerative colitis - People with ulcerative colitis have ulcers and irritation in the colon and rectum. This condition increases the risk of cholangiocarcinoma.
This content has been reviewed and approved by Myo Thant, MD.