According to our center’s data, patients with MTC combined with PTC who have a smaller tumor diameter, especially those with a diameter of < 1 cm, have lower calcitonin and carcinoembryonic antigen levels, a lower risk of postoperative recurrence, a lower proportion of lymph node metastases and a better prognosis. The gene discussed is CALCA; the disease is medullary thyroid gland carcinoma.