We have studied the sorting and alteration of the thyroglobulin (tg) secreted by well-differentiated carcinomas using a group of anti-tg monoclonal antibodies. A previously described monoclonal antibody, specific for the hormogenic iodinated epitopes, shows that in carcinomas the iodinated tg is not secreted in the colloid as in normal glands but is accumulated in the cytoplasm of the cells. Separation of tg in a concanavalin A column, to isolate the correctly glycosilated protein, reveals that hormogenesis is present only in glycosilated tg with a correct final configuration. An other monoclonal antibody, specific for an epitope connected with the carbohydrate moiety of the tg, reacts with tgs from normal glands and from any thyroid lesion except tg from carcinomas. This tg of carcinomas presents an alteration in the oligosaccharide chains that can be detected by this antibody. The alteration is specific for malignant tumors and could be connected with the missing exocytosis of the iodinated tg in carcinomas.
