Involucrin, a Marker of Squamous and Urothelial Differentiation. An Immunohistochemical Study on Its Distribution in Normal and Neoplastic Tissues

Involucrin is a soluble protein precursor of the cross-linked envelope present in the submembranous zone of human stratum corneum, and subsequently demonstrated in stratified squamous epithelia. The immunoperoxidase technique was used to assess the distribution of involucrin in 107 normal and 318 abnormal tissues. With few exceptions, involucrin was restricted to squamous epithelia, urothelium, some skin appendages and thymic Hassall's corpuscles. In normal squamous epithelium and normal urothelium, staining was most intense in the superficial layers where it was concentrated at the cell periphery and gradually decreased toward the basal layer. This orderly staining pattern was maintained in benign squamous and urothelial lesions and in grade I papillary urothelial carcinomas. Higher grade papillary urothelial carcinomas, infiltrating urothelial and squamous carcinomas, and in situ urothelial and squamous carcinomas demonstrated abnormal staining patterns for involucrin that are described. Foci of squamous differentiation in adenocarcinomas and other epithelial malignancies stained intensely for involucrin. Brenner tumours of the ovary and Walthard rests of the fallopian tube, lesions of uncertain histogenesis but possibly urothelial-related, also stained for involucrin. Results of this study suggest that involucrin is a sensitive and specific marker for squamous and urothelial differentiation, staining patterns for involucrin may be helpful in distinguishing benign from malignant urothelial and squamous lesions, and presence of involucrin may be helpful in determining the histogenesis of selected lesions.