Histogenesis of thyroid carcinoma.

Follicular and papillary thyroid carcinoma have for many years been regarded as biologically distinct from medullary thyroid carcinoma. The recent recognition of a tumor type which is morphologically and functionally intermediate between these two categories suggests however that differentiated thyroid carcinoma may be regarded as a continuous spectrum of tumor types all of which are derived from a common thyroid stem cell, capable of developing both follicular and parafollicular tumor cells, as well as intermediate cell forms. It is also proposed that anaplastic giant cell thyroid carcinoma represents a heterogeneous group consisting of the anaplastic counterparts not only to follicular and papillary carcinoma but also to the intermediate type and to classical medullary carcinoma.