Types of thyroid cancer

There are five main types of thyroid cancer. The type of cancer is based on what the cells look like under a microscope. Your treatment will depend on which type of thyroid cancer you have.

• Papillary thyroid cancer (PTC). This is the most common type of thyroid cancer, making up 80% to 85% of all thyroid cancers.¹ It is most commonly diagnosed in people who are in their 30s and 40s. PTC starts in cells called follicular cells and usually is only found in one lobe of the thyroid. Although PTC usually grows very slowly, it often spreads to lymph nodes in the neck. With treatment, long-term survival is approximately 98%.²
• Follicular thyroid cancer (FTC). This is the second most common type of thyroid cancer, making up 5% to 10% of thyroid cancer cases.¹ It is most commonly diagnosed in people who are in their 50s and is usually found in countries where people do not get enough iodine from food. FTC usually remains in the thyroid but can spread to the lungs. With treatment, long-term survival is approximately 92%.²
• Medullary thyroid cancer (MTC). About 3% to 12% of thyroid cancers are medullary thyroid cancers.¹ This is the only type of thyroid cancer that develops from the C cells of the thyroid gland. By the time it is diagnosed, it may already have spread to the liver, lungs, and lymph nodes. The long-term survival rate is about 80% if the whole thyroid gland is removed (thyroidectomy) and the cancer has not spread to nearby lymph nodes. But if the cancer is not detected at an early stage, the survival rate drops. There are two types of MTC: sporadic and familial.^{3, 4}
  • Sporadic MTC occurs mostly in adults, does not occur in families, and usually affects only one lobe of the thyroid gland.
  • Familial MTC can develop during early childhood, occurs in families, and can spread to other parts of the body. There are three types of familial thyroid cancer, called MEN 2a, MEN 2b, and FMTC (familial medullary thyroid cancer). Genetic blood tests can be used to identify people who are at risk for developing familial medullary cancer. If genetic testing shows a gene problem called RET mutation, most experts suggests surgery to remove the thyroid to help prevent future medullary thyroid cancer.
• Anaplastic carcinoma. This is a very rare and aggressive form of thyroid cancer. About 1% to 3% of thyroid cancers are anaplastic.¹ By the time it is diagnosed, it usually has spread to the neck and other parts of the body. It grows rapidly and is the most fatal form of thyroid cancer. Anaplastic carcinoma is more common in women older than 50.
• Thyroid lymphoma. This rare type of lymphoma starts in the thyroid gland and causes it to grow larger. Fewer than 1% of thyroid cancers are this type.¹ It is more common in older women and people with Hashimoto's thyroiditis.⁵

Citations

1. Carling T, Udelsman R (2005). Thyroid tumors section of Cancer of the endocrine system. In VT DeVita Jr et al., eds., Cancer: Principles and Practice of Oncology, 7th ed., pp. 1502–1520. Philadelphia: Lippincott Williams and Wilkins.

2. Sherman SI (2003). Thyroid carcinoma. Lancet, 361(9356): 501–511.

3. Shaha AR (2000). Controversies in the management of thyroid nodule. Laryngoscope, 110(2, Part 1): 183–193.

4. National Cancer Institute (2007). Genetics of Medullary Thyroid Cancer (PDQ): Treatment-Health Professional Version. Available online: http://www.cancer.gov/cancertopics/pdq/genetics/medullarythyroid/healthprofessional.

5. Utiger RD (2003). Thyroid cancer. In B Furie et al., eds., Clinical Hematology and Oncology, pp. 1117–1127. Philadelphia: Churchill Livingstone.