Cancer begins in cells, the building blocks that make up tissues. Tissues make up the organs of the body.

Normal cells grow and divide to form new cells as the body needs them. When normal cells grow old or get damaged, they die, and new cells take their place.

Sometimes, this process goes wrong. New cells form when the body doesn't need them, and old or damaged cells don't die as they should. The buildup of extra cells often forms a mass of tissue called a growth, nodule, or tumor.

Growths in the liver can be benign (not cancer) or malignant (cancer). Benign tumors are not as harmful as malignant tumors:

• Benign tumors:
  • are rarely a threat to life
  • can be removed and usually don't grow back
  • don't invade the tissues around them
  • don't spread to other parts of the body
  
  
• Malignant growths:
  • may be a threat to life
  • sometimes can be removed but can grow back
  • can invade and damage nearby tissues and organs (such as the stomach or intestine)
  • can spread to other parts of the body

Most primary liver cancers begin in hepatocytes (liver cells). This type of cancer is called hepatocellular carcinoma or malignant hepatoma.

Liver cancer cells can spread by breaking away from the original tumor. They mainly spread by entering blood vessels, but liver cancer cells can also be found in lymph nodes. The cancer cells may attach to other tissues and grow to form new tumors that may damage those tissues. See the Staging section for information about liver cancer that has spread.

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