What causes a thyroid nodule?
Thyroid cancer is the most important cause of a thyroid nodule. Fortunately, cancer occurs in less than 10% of nodules (see the Thyroid Cancer brochure). This means that about 9 of 10 nodules are benign (noncancerous); these include colloid nodules, follicular neoplasms, and thyroid cysts. Autonomous nodules, which overproduce thyroid hormone, can occasionally lead to hyperthyroidism. We do not know what causes most noncancerous thyroid nodules to grow.