Paraffin sections of 106 primary thyroid carcinomas were the subject of an immunocytochemical study to determine the density of infiltrates of S-100 protein-positive dendritic/Langerhans cells (LC), lysozyme-positive histiocytes, and LCA-positive lymphocytes. Evidence of dense infiltrates of LCs was found only in the majority of papillary thyroid carcinomas (PCs). The determination of the quantity of LCs proved to be a highly effective means of assessing the prognosis of these tumors. Irrespective of other morphologic and clinical features, no single instance of death resulting from cancer occurred among 23 PCs with dense LC infiltrates (including 6 tumors of stage pT4), while 9 of 53 (17%) of the remaining patients ultimately died from thyroid cancer. On the other hand, the degree of histiocytic and lymphocytic infiltrations was not associated with a distinct biologic behavior neither among PC nor among the remaining thyroid carcinomas. These findings suggest that LCs may play an important role in the immunologic defense mechanisms of the host against the tumor only in the papillary type of thyroid cancer.
