Tumor bed of laryngectomy and thyroid tumor, H&E stain and calcitonin immunostains. (a) H&E stain ×400: tumor bed, laryngectomy: solitary nerve twig infiltrated by plump epithelioid tumor cells. (b) Calcitonin immunostain ×400: tumor bed, laryngectomy: the infiltrating tumor cells are strongly immunoreactive for calcitonin. (c) H&E stain ×100: thyroid, right lobe nodule: 4 mm tumor nodule (left) adjacent to pink colloid-filled thyroid follicles (right). (d) Calcitonin immunostain ×400: thyroid: tumor cells are strongly reactive for calcitonin and can be seen focally invading into benign thyroid follicles.