Liver cancer develops when some cells begin to grow abnormally. While it's not clear why this occurs, it is believed that cancer occurs when there has been damage to the DNA, which is the substance that stores the instructions for every chemical process in your body, including the rate of cellular growth. When damage occurs to your DNA, cells may grow out of control and eventually form a tumor.

The following factors may damage the DNA in liver cells:

Cirrhosis

Excessive use of alcohol is the most common cause of cirrhosis in the United States. Cirrhosis results in irreversible scarring in the liver. Hereditary hemochromatosis, which causes excess iron to collect in your liver and other tissues, can also lead to cirrhosis.

Hepatitis B and C

The most common cause of liver cancer worldwide, is chronic infection with the hepatitis B virus (HBV) or hepatitis C (HCV). In the United States, hepatits C infection is responsible for half the new cases of hepatocellular carcinoma, the most frequent cause of primary liver cancer. Most cases of hepatitis C is spread through blood transfusions that hasn't been screened for the virus, through needles used in tattooing or body piercing or through sexual transmission. HBV is transmitted primarily through unprotected sex and contaminated needles. Women infected with HBV can pass the virus on to their unborn children.

Primary billiary cirrhosis

This condition involves an inflammation of the bile ducts in the liver and produces a sharp increase in an individual's risk for cholangiocarcinoma, a type of primary liver cancer. People with this condition should undergo routine cancer screening tests.

Long-term exposure to aflatoxins

Although the risk of exposure to aflatoxins in the United States is small, the toxins have been found in corn and corn products, peanuts and peanut products, cottonseed, milk, Brazil nuts, pecans, pistachios and walnuts. These are highly toxic carcinogens that can develop when certain crops or foods are contaminated with the fungus Aspergillus flavus. Aflatoxins can damage the P53 gene, which functions to prevent excessive cell growth. The Food and Drug Administration has implemented several procedures to monitor and identify aflatoxins in the food supply.

Vinyl chloride and thorium dioxide (Thorotrast)

Vinyl chloride is a chemical used to manufacture plastics. At one time, Thorotrast was given to people undergoing X-ray tests. Both chemicals have been associated with the development of rare cancers that start in the liver's blood vessels.

Arsenic

Arsenic, a known carcinogen, can lead to the development of liver cancer. Arsenic is odorless and tasteless and can enter drinking water supplies from natural deposits in the earth or from agricultural and industrial practices. The EPA has set the arsenic standard for drinking water at .010 parts per million (10 parts per billion) to protect consumers served by public water systems from the effects of long-term, chronic exposure to arsenic. 

Ulcerative colitis

This is an inflammatory condition of the colon and digestive tract which can cause changes within the bile ducts and raises your risk of cholangiocarcinoma, a type of primary liver cancer.