ABNORMAL INTRACELLULAR AND EXTRACELLULAR DISTRIBUTION OF BASEMENT-MEMBRANE MATERIAL IN PAPILLARY CARCINOMA AND HYALINIZING TRABECULAR TUMORS OF THE THYROID - IMPLICATION FOR DEREGULATION OF SECRETORY PATHWAYS

Papillary carcinoma (PC) and hyalinizing trabecular tumors (HTT) of th e thyroid share several morphological features, including the presence of nuclear pseudoinclusions (NPI). One of the distinct characteristic s of HTT is its hyalinizing stroma, which contains abundant basement m embrane (BM) material. We investigated the distribution of BM material in PC and HTT. Fifteen cases of PC and nine cases of HTT were analyze d immunohistochemically with monoclonal antibodies for type IV collage n and laminin. Three stromal staining patterns were observed: (1) line ar staining along the epithelium lining papillae, between trabeculae, and around follicles; (2) focal absence of staining; (3) lumpy or diff use stromal staining. Although the latter was more commonly seen in HT T, all three patterns were present in both tumor types. More interesti ngly, we observed two hitherto undescribed intracellular staining patt erns in both tumor types: intracytoplasmic dotlike staining and staini ng of NPI. Electron microscopy was performed in three cases of PC. Dil ated cisternae of endoplasmic reticulum containing dense amorphous mat erial resembling BM were observed in the cytoplasm in one case and in the NPI in another. These findings suggest the presence of a common pa thway for the abnormal production of BM in both PC and HTT. Two mechan isms that may account for the abnormal intracellular detection of BM m aterials are proposed: (1) intracellular invagination/phagocytosis of extracellular matrix by the tumor cells; (2) abnormal production or al teration in secretory pathway in tumor cells resulting in intracellula r accumulation and intranuclear invagination. The combination of immun ohistochemical and electron microscopic findings favors the latter. Th e similar patterns of BM deposition shared by PC and HTT further suppo rt the hypothesis that PC and HTT are related to each other. Copyright (C) 1997 by W.B. Saunders Company.