Thyroid cancer is a cancerous growth of the thyroid gland.

Thyroid cancer can occur in all age groups.

People who have had radiation therapy to the neck are at higher risk. Radiation therapy was commonly used in the 1950s to treat enlarged thymus glands, adenoids and tonsils, and skin disorders. People who received radiation therapy as children are at increased risk for getting thyroid cancer.

Other risk factors are a family history of thyroid cancer and chronic goiter.

There are several types of thyroid cancer:

• Anaplastic carcinoma (also called giant and spindle cell cancer) is the most dangerous form of thyroid cancer. It is rare, and does not respond to radioiodine therapy. Anaplastic carcinoma spreads quickly and invades nearby structures such as the windpipe (trachea), causing breathing difficulties.
• Follicular carcinoma accounts for about 30% of all cases and is more likely to come back and spread.
• Medullary carcinoma is a cancer of nonthyroid cells that are normally present in the thyroid gland. This form of the thyroid cancer tends to occur in families. It requires different treatment than other types of thyroid cancer.
• Papillary carcinoma is the most common type, and usually affects women of childbearing age. It spreads slowly and is the least dangerous type of thyroid cancer.