Part of “CHAPTER 41 – UNUSUAL THYROID CANCERS“

Rarely, thyroid cancers may display features of both medullary and follicular carcinoma.42 These tumors are distinct from medullary cancer with normal “trapped” follicles and are characterized by distinct regions of medullary carcinomas adjacent to follicular or papillary cancer. The pathogenesis of these tumors is not clear. Their occurrence suggests a similar response of follicular and parafollicular cells to an oncogenic stimulus rather than the presence of a common progenitor cell. However, cells expressing both thyroglobulin and calcitonin have been identified.42 The presence of mutations in the ret oncogene, typical of medullary cancer, have not been studied, but familial occurrence of these tumors has been described.43,44