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).