The histological features of medullary carcinoma are illustrated in Fig. 1 to Fig. 8. These include nests or chords of cells penetrating dense pink stroma with a lobular, trabecular or even solid growth pattern (Figs 1, 2, 3 and 4). Areas of calcification can also be seen (Fig. 1). The tumor can be seen to abut normal thyroid microscopically ( Fig. 2). On higher power, the neoplastic cells appear to show round, relatively uniform cells with a punctuate chromatin pattern. The cytoplasm is slightly basophilic with fine membrane granules. There is focal staining of the stroma with Congo red (Fig. 5). There is moderate cytoplasmic staining for Calcitonin (Fig. 7). The staining for CEA is intensely positive in all tumor cells (Fig. 6).