The causes of thyroid cancer aren't fully understood at present. Certain factors that make developing thyroid cancer more likely include a history of non-cancerous (benign) thyroid disease, e. g an enlarged thyroid or inflammation of the thyroid; radiotherapy to the neck particularly if this was done at a young age; not enough iodine in the diet; an inherited bowel condition called familial adenomatous polyposis (FAP) or family history of medullary thyroid cancer.
Attribution: BUPA