Thyroid cancer typically doesn't cause any signs or symptoms early in the disease. As thyroid cancer grows, it may cause:

• A lump that can be felt through the skin on your neck
• Changes to your voice, including increasing hoarseness
• Difficulty swallowing
• Pain in your neck and throat
• Swollen lymph nodes in your neck

It's not clear what causes thyroid cancer.

Thyroid cancer occurs when cells in your thyroid undergo genetic changes (mutations). The mutations allow the cells to grow and multiply rapidly. The cells also lose the ability to die, as normal cells would. The accumulating abnormal thyroid cells form a tumor. The abnormal cells can invade nearby tissue and can spread throughout the body.

Types of thyroid cancer

The type of thyroid cancer you have determines treatment and prognosis. Types of thyroid cancer include:

• Papillary thyroid cancer. The most common form of thyroid cancer, papillary thyroid cancer arises from follicular cells, which produce and store thyroid hormones. Papillary thyroid cancer can occur at any age, but most often it affects people ages 30 to 50.
• Follicular thyroid cancer. Follicular thyroid cancer also arises from the follicular cells of the thyroid. It usually affects people older than age 50. Hurthle cell cancer is a rare and potentially more aggressive type of follicular thyroid cancer.
• Medullary thyroid cancer. Medullary thyroid cancer begins in thyroid cells called C cells, which produce the hormone calcitonin. Elevated levels of calcitonin in the blood can indicate medullary thyroid cancer at a very early stage. Certain genetic syndromes increase the risk of medullary thyroid cancer, although this genetic link is uncommon.
• Anaplastic thyroid cancer. Anaplastic thyroid cancer is a rare and rapidly growing cancer that is very difficult to treat. Anaplastic thyroid cancer typically occurs in adults age 60 and older.
• Thyroid lymphoma. Thyroid lymphoma is a rare form of thyroid cancer that begins in the immune system cells in the thyroid and grows very quickly. Thyroid lymphoma typically occurs in older adults.

Factors that may increase the risk of thyroid cancer include:

• Female sex. Thyroid cancer occurs more often in women than in men.
• Exposure to high levels of radiation. Examples of exposure to high levels of radiation include radiation treatments to the head and neck and fallout from sources such as nuclear power plant accidents or weapons testing.
• Certain inherited genetic syndromes. Genetic syndromes that increase the risk of thyroid cancer include familial medullary thyroid cancer and multiple endocrine neoplasia.

Thyroid cancer that comes back

Despite treatment, thyroid cancer can return, even if you've had your thyroid removed. This could happen if microscopic cancer cells spread beyond the thyroid before it's removed.

Thyroid cancer may recur in:

• Lymph nodes in the neck
• Small pieces of thyroid tissue left behind during surgery
• Other areas of the body

Thyroid cancer that recurs can be treated. Your doctor may recommend periodic blood tests or thyroid scans to check for signs of a thyroid cancer recurrence.