[Implications of electron microscopy and immunohistochemistry data in the concept of mixed tumors of the thyroid]

The role played by the ultimobranchial body in the histogenesis of thyroid tumors is discussed in the light of the results of studies of several types of thyroid carcinomas: poorly differentiated intermediate carcinomas, medullary carcinomas with thyroglobulin immunoreactivity, and mucoepidermoid carcinomas with "follicular" and "parafollicular" differentiation.