RET and medullary thyroid gland carcinoma: Three patients with RET mutation underwent prophylactic total thyroidectomy with the histological diagnosis of medullary thyroid cancer (all three patients were 6 years old or less); the preoperative calcitonin levels were respectively 3.4 pg/ml, 7 pg/ml and 2.2 pg/ml (mean 4.2 pg/ml).