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 or tumor.

Tumors in the mouth or throat 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 tumors:
  • may be a threat to life
  • can grow back after they are removed
  • can invade and damage nearby tissues and organs
  • can spread to other parts of the body

Almost all oral cancers begin in the flat cells (squamous cells) that cover the surfaces of the mouth, tongue, and lips. These cancers are called squamous cell carcinomas.

Oral cancer cells can spread by breaking away from the original tumor. They enter blood vessels or lymph vessels, which branch into all the tissues of the body. The cancer cells often appear first in nearby lymph nodes in the neck. The cancer cells may attach to other tissues and grow to form new tumors that may damage those tissues.

The spread of cancer is called metastasis. See the Staging section for information about oral cancer that has spread.

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