Human medullary thyroid carcinoma. Initial characterization and in vitro differentiation of two new cell lines.

Medullary carcinoma of the thyroid (MCT), a tumor of calcitonin (CT)-secreting C cells, can display a variable malignant potential with poor prognosis linked to decreased cell differentiation. In vitro study of MCT has been hampered by the fact that few cell lines derived from this neoplasm have been available for study. Herein are reported the characteristics of two new lines derived from human MCT that are tumorigenic in athymic mice and do not secrete CT. After treatment with various concentrations of retinoic acid (a vitamin A derivative) and cyclic adenosine monophosphate, both lines exhibit the traits of more differentiated cells with a decrease in cellular proliferation and an increase in cytoplasmic CT content as shown by in situ immunoperoxidase staining. These cell lines should prove of great value in the study of the biology of MCT and the mechanisms underlying induced differentiation in this type of tumor.