 Calcitonin is produced by the "C" cells of the thyroid, which, because they are always hyperplastic or malignant in MEN2B, produce more calcitonin than normal.Calcitonin levels remain a valuable marker to detect recurrence of medullary thyroid carcinoma after thyroidectomy.Luxol fast blue staining identifies myelin sheathing of some fibers, and lesional cells react immunohistochemically for S-100 protein, collagen type IV, vimentin, NSE, and neural filaments.