What is thyroid cancer?

Last medical review:

Thyroid cancer starts in the cells of the thyroid. A cancerous (malignant) tumour is a group of cancer cells that can grow into nearby tissue and destroy it. The tumour can also spread (metastasize) to other parts of the body.

The thyroid is part of the endocrine system. It is a small gland in the front of the neck below the larynx (voice box) and near the trachea (windpipe). It has a right and left lobe, one on each side of the trachea. The lobes are joined by a thin piece of tissue called the isthmus.

Diagram of the location and structure of the thyroid gland
Diagram of the location and structure of the thyroid gland

Cells in the thyroid sometimes change and no longer grow or behave normally. These changes can lead to non-cancerous (benign) conditions such as hypothyroidism, hyperthyroidism, thyroid nodules or goitre.

Sometimes changes to thyroid cells can cause cancer. The most common type of thyroid cancer is papillary thyroid cancer. Follicular thyroid cancer (which includes Hurthle cell thyroid cancer) is the second most common type, but it develops much less often than papillary thyroid cancer. Medullary and anaplastic thyroid cancers can also develop, but they are less common.

Other very rare types of cancer can also start in the thyroid gland, including non-Hodgkin lymphoma and soft tissue sarcoma.

Expert review and references

  • Shereen Ezzat, MD, FRCPC, FACP
  • Davidson BJ, Newkirk KA, Burman KD . Cancer of the thyroid and the parathyroid: general principles and management. Harrison LB, Sessions RB, Kies MS (eds.). Head and Neck Cancer: A Multidisciplinary Approach. 4th ed. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins; 2014: 28A:779-824.
  • American Cancer Society. Thyroid Cancer Early Detection, Diagnosis, and Staging . 2019: https://www.cancer.org/.
  • Kotwal A, Davidge-Pitts CJ, Thompson GB. Thyroid Tumors. DeVita VT Jr., Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg's Cancer: Principles & Practice of Oncology. 11th ed. Philadelphia, PA: Wolters Kluwer; 2019: 81:1326–1337.
  • PDQ® Adult Treatment Editorial Board. Thyroid Cancer Treatment (PDQ®) – Patient Version. Bethesda, MD: National Cancer Institute; 2021: https://www.cancer.gov/.
  • American Society of Clinical Oncology (ASCO). Cancer.net: Thyroid Cancer. 2021: https://www.cancer.net/.

The thyroid

Thyroid cancer starts in the thyroid gland. It is in the neck, makes hormones and is part of the endocrine system.

Cancerous tumours of the thyroid

The most common types are papillary thyroid cancer (papillary carcinoma) and follicular thyroid cancer (follicular carcinoma).

Non-cancerous conditions of the thyroid

Hypothyroidism, hyperthyroidism, thyroid nodules, thyroiditis and goitre are the most common non-cancerous thyroid conditions.