4a. Irregular clusters of medullary thyroid carcinoma cells with clear
to faint eosinophilic cytoplasm. These cell clusters were comparatively
smaller than adjacent normal follicles and focal amyloid was seen in the
left superior corner (H&E stain, x100).
4b. Calcitonin stained positively in the carcinoma but also increased
number of C cells in adjacent follicles (x20).