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Desmosome Ultrastructure and the Biological Behavior of Chemical Carcinogen-induced Urinary Bladder Carcinomas¹

Department of Pathology, Rush Medical College and Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612 [B. U. P., J.A., R. S. W.], and The St. Vincent Hospital at the University of Massachusetts, Worcester, Massachusetts 01610 [S. M. C.]

In this quantitative electron microscopic study, we examined the relationship of desmosomes to tumor invasiveness in chemical carcinogen (N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide)-induced urinary bladder transitional cell carcinomas in the Fischer rat. The number of desmosomes per unit area of plasma membrane was significantly reduced in carcinomas. However, the percentage of cell surface area occupled by desmosomes was greater in carcinomas than in controls. This was accounted for on the basis of increases in desmosomal size, which result from squamous differentiation within the tumors. Areas of transitional cell differentiation and squamous differentiation demonstrated an equal capacity for invasiveness. Desmosomes were abundant in invading nests of tumor cells. These findings cast doubt on the validity of the concept of decreased intercellular adhesion as a prerequisite for tumor invasion, since strong interadhesion is probably a function of the area occupied by the intercellular junctions.

¹ This work was supported by funds from the Otho S. A. Sprague Memorial Institute and National Cancer Institute Grant CA-15945.

² To whom requests for reprints should be addressed, at Department of Pathology, Rush Medical College, 1753 W. Congress Parkway, Chicago, III. 60612.

Received 3/ 8/78. Accepted 7/ 6/78.