The follicular cell-differentiated carcinomas account for some eighty per cent of the total number of thyroid carcinomas, and the anaplastic carcinomas only fifteen per cent. The incidence of medullary carcinomas varies from five per cent to ten per cent, while that of malignant lymphomas is less than two per cent. Secondary tumours are often found at post-mortem as microscopic deposits, sometimes within benign thyroid nodules.
A histopathological classification of thyroid malignancies is shown in Fig. 16.1.
