In 1988, the World Health Organization established the name and diagnostic criteria of MMFCC for the first time, which was defined as a mixed carcinoma of follicular epithelial cell origin that showed both calcitonin immunopositive MTC and thyroglobulin immunopositive follicular epithelial cell-derived malignant tumors (Hedinger et al. 1988). The gene discussed is CALCA; the disease is medullary thyroid gland carcinoma.