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Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer (85%-to-90% of all liver cancers) and occurs when liver cells (hepatocytes) develop abnormalities and turn cancerous. Hepatocellular carcinoma most frequently occurs in people with chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) infections or non-alcoholic fatty liver disease (NAFLD). Most people diagnosed with hepatocellular carcinoma also have cirrhosis, a chronic liver disease that causes scarring (fibrosis) in the liver, which is a type of chronic liver damage. While rare in the U.S., the number of people diagnosed with hepatocellular carcinoma has increased in the past few decades. In other parts of the world, especially Asia, hepatocellular carcinoma occurs much more frequently due to an increased exposure to hepatitis B virus, cancer-causing chemicals, and parasitic infections (schistosomiasis). Primary hepatocellular carcinoma is cancer that originates in the liver. Secondary liver cancers occur when the cancer has spread to the liver from another part of the body, usually the breast, colon, lung, or pancreas and are different than primary hepatocellular carcinoma, which may begin as a tumor that eventually spreads to other areas of the liver.