Thyroid carcinomas with mixed follicular and C-cell differentiation patterns

Divergent endocrine-neuroendocrine differentiation in thyroid carcinoma occ urs in mixed medullary-follicular carcinomas (MMFC). Less than 40 cases of MMFC have been reported having highly heterogeneous patterns of growth, Cla ssical medullary carcinoma areas may be intermingled with follicles or papi llae or even oxyphilic and solid areas, Calcitonin and thyroglobulin are ex pressed in different cell populations. Presence of the latter suggests a po tential usefulness of radioiodine treatment. The clinical behavior of MMFC does not differ from that of ordinary medullary carcinoma, The histogenesis of MMFC is controversial. The genetic analysis of the 2 neoplastic compone nts showed that they are not derived from a common precursor, but rather di splay remarkable differences in the genetic profile (RET mutations and alle lic losses). In addition, in some cases the follicular component was found to be oligo/polyclonal and therefore possibly hyperplastic rather than neop lastic. The follicular cells may have grown into the medullary carcinoma, a fter acquiring some molecular defect, being "hostage" of the true neoplasti c (medullary) component. Copyright (C) 2000 by W.B. Saunders Company.