The structure of tight junctions in human thyroid tumors. A systematic freeze-fracture study.

Tight junctions of normal human epithelium comprise 6--8 intramembranous ridges. Tight junctions of adenomas and one case of follicular carcinoma were morphologically identical with normal controls. Another follicular carcinoma (clinically less malignant than the case mentioned above), however, showed loss of junctional polarity with spreading of ridges on lateral cell membranes. One case of papillary carcinoma (clinically low malignancy) displayed only focal attenuations of the tight junction belt. Another more malignant tumor of the same histologic type showed breaks of ridges and focal interruptions of the tight junction meshwork. Cell membranes of two anaplastic carcinomas of high malignancy were completely devoid of tight junction ridges. We conclude that tight junction alterations are not necessarily implicated in malignant transformation and that they correspond with tumor differentiation rather than directly with a single parameter of thyroid tumor malignancy.