N-myc expression in neoplasia of human thyroid C-cells.

In view of the frequent reports of the increased expression of myc oncogenes in several neuroendocrine tumor types, we have investigated c- and N-myc expression in human medullary carcinoma, a malignant tumor derived from the neuroendocrine "C"-cell subpopulation of the thyroid gland. In situ nucleic acid hybridization was used to permit analysis not only of tumors but also of normal C-cells which form a tiny, scattered, minority of the thyroid epithelial cell population. N-myc expression was readily demonstrable in 6 of 21 tumor samples and c-myc in one case, whereas neither N- nor c-myc mRNA was ever detected in normal C-cells. We conclude that N-myc expression is a specific feature of C-cell tumors and is not merely a differentiation marker of their cell of origin. The data therefore strengthen the hypothesis that myc oncogene activation plays a role in neuroendocrine neoplasia.