MUC5AC and medullary thyroid gland carcinoma: They correspond to the mixed neuroendocrine-non-neuroendocrine tumors of other organs (e.g., pancreatic mixed neuroendocrine neoplasms), and need to be distinguished from collision MTC-follicular cell-derived tumors and from the rare amphicrine MTC variant where cytoplasmic mucin accumulates within neoplastic C-cells [76].