Altered gap and tight junctions in human thyroid oncocytic tumors: A studyof 8 cases by freeze-fracture

Human oncocytic tumors of the thyroid gland may be either adenomas or carci nomas. The morphology and the ultrastructure of these oncocytes are well-kn own. Numerous studies have demonstrated the role of gap and tight junctions in experimental and human carcinogenesis; however, the junctional complexe s of the oncocytic tumors have never been studied. The aim of this study is to analyze gap and tight junctions in the oncocytic tumors of the thyroid. Because they are morphologically similar, whether benign or malignant, the y offer an attractive model for studying the junctional complexes in both b enign and malignant lesions. Eight oncocytic human thyroid tumors were coll ected and studied by freeze-fracture. Four of these cases were benign and f our were malignant. Four cases of normal gland were also studied to represe nt the control group. Normal tight and gap junctions were described for the control group. No gap junctions could be found for the oncocytic tumors. F urthermore, alterations of the tight junctions were described; especially f ocal tights in the oncocytic adenomas and well organized and labyrinthic ti ght junctions in the oncocytic carcinomas. The lack of gap junction in the benign as well as in the malignant oncocytomas may suggest that the absence of gap junction is not sufficient for malignancy. The alterations of the t ight junctions found in the oncocytic tumors of the thyroid are similar to those observed in poorly differentiated tissues or tumors, and may suggest a cellular regression rather than a tumorogenic factor.