Urothelial Carcinoma-In-Situ : CK20

Comments:
Urothelial Carcinoma-In-Situ vs Reactive Urothelial Atypia: The distinction of urothelial CIS from reactive lesions is usually straightforward and is based on morphology, especially nuclear features. In challenging cases, an immunohistochemical panel consisting of CK20, p53, and CD44 can be used. Following patterns are noticed:

Normal Urothelium: CK20+ in umbrella cells only; p53 negative; CD44+ in basal/parabasal urothelium
Reactive Atypia: CK20+ in umbrella cells only; p53 negative; CD44+ full thickness
Urothelial CIS: CK20+ diffuse, full thickness; p53+ diffuse, nuclear, full thickness; CD44 negative.

Note: These staining patterns are not absolute or consistent and show considerable overlap. They must be interpreted in the context of morphology. The panel cannot be used to distinguish between dysplasia and CIS. In this image, the top half shows urothelial CIS in a patient who presented with microscopic hematuria. The underlying Brunn nests are not involved. The lower half is CK20 immunostain showing full thickness staining of CIS. The underlying benign Brunn's nests are CK20 negative.