It is not clear what causes thyroid cancer, but factors that may increase the risk of thyroid cancers include:

• Being female – thyroid cancer affects more women than men
• A family history of thyroid cancer
• Exposure to high levels of radiation – e.g. radiation therapy
• Certain inherited genetic conditions such as familial medullary thyroid cancer, multiple endocrine neoplasia, Cowden’s syndrome and familial adenomatous polyposis