S-100 protein is a differentiation marker in thyroid carcinoma of follicular cell origin: An immunohistochemical study

S-100 protein, a dimer of S-100α and S-100β subunits (S-100α and S-100β), is widely distributed in human tissue, and several papers describing S-100 protein expression in follicular cells of the thyroid have been published. in the present study, 105 cases of thyroid carcinoma (of which 96 were papillary, four follicular, two undifferentiated, and three meduilary) were analyzed immunohistochemically for the expression of S-100 protein, S-100α, S-100β, and thyroglobulin. in papillary carcinoma, 188 lesions were studled and classified into well differentiated types (56 papillary, 45 follicular) and poorly differentiated types (41 trabecular, four solid, eight squamoid, three tall, and one insular), because the histological structure of each tumor was heterogeneous. The percentage of lesions which expressed positively for 5–100 protein and S-100α, respectively, according to type were: papillary, 96 and 99%; foillcular, 96 and 100%; trabecular, 95 and 100%; solid, 50 and 50%; squamoid, 50 and 757%; and tall, 33 and 100%. The insular type was negative for both. For papillary carcinoma, well differentiated lesions showed stronger S-100α expression than poorly differentiated lesions. S-100α expression was weaker In follicular and undifferentiated carcinoma than in papillary carcinoma. Meduliary carcinoma also expressed S-100α. S-100β was positive in lesions that expressed S-100α strongly. Expression of S-100 protein and S-100α protein correlated with thyroglobulin synthesis in the follicular cells. It was concluded that S-100 protein, mainly S 100α. exists in thyroid follicular cells, that it exists In higher quantity in most of the well differentiated lesions but in lower quantity in poorly differentiated or Undifferentiated lesions, and that 5100 protein, especially S-100α, is a differentiation marker in carcinoma of thyroid follicular cell origin.