[Cytokeratins in inverted papillomas of the urinary bladder. (Part 1.)]

Inverted papilloma (transitional cell papilloma, inverted type) is a rare, benign urothelial tumor. The distribution of cytokeratin (CK) expression in 22 cases was investigated and compared with normal urothelium and urothelial carcinomas: CK7/8, basal increased positivity; CK13, diffuse positivity; CK18, loss of intensity and loss of umbrella cell staining; CK19, reduction of positivity; CK20, reduction of umbrella cell staining. The data indicate that the inverted papilloma is a basal cell urothelioma.