In vitro responsiveness to serum growth factors is inversely related to in vivo malignancy in human thyroid epithelial cells.

We have examined the proliferative response (DNA synthesis) of primary thyroid epithelial cultures to serum and a defined serum-substitute. These cultures were derived from normal human thyroid and from thyroid adenomas and carcinomas. All normal cultures showed a dose-dependent response, with a maximum 3H-thymidine labelling index of around 50%. Three out of the four adenomas demonstrated a much reduced or delayed response under the same conditions. In two carcinomas, labelling was never more than 5% and in one case was undetectable. This inverse relationship between the degree of in vivo malignancy and proliferative response in vitro has important implications for the interpretation of tissue culture models of epithelial neoplasia and also offers the potential for isolating novel growth factors specific for thyroid cancer cells.