Normal thyroid 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 does not need them, and old or damaged cells do not die as they should. The buildup of extra cells often forms a mass of tissue called a nodule. It may also be called a growth or tumor.
- Benign nodules:
- Are usually not harmful
- Don’t invade the tissues around them
- Don’t spread to other parts of the body
- Usually don’t need to be removed
- Malignant nodules (thyroid cancer):
- May sometimes be a threat to life
- Can invade nearby tissues and organs
- Can spread to other parts of the body
- Often can be removed or destroyed, but sometimes thyroid cancer returns
Thyroid cancer cells can spread by breaking away from the thyroid tumor. They can travel through lymph vessels to nearby lymph nodes. They can also spread through blood vessels to the lungs, liver, or bones. After spreading, 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 thyroid cancer that has spread.