CK20 and CK5/6 Immunohistochemical Staining of Urothelial Neoplasms: A Perspective

Figure 8

(a) Cartoon depicting stages of differentiation during the embryologic development of the urothelium. During the early stages, the developing urothelium retains CK20 expression normally seen in the cloaca. During this stage, no basal layer is present. (b) During the development of urothelium, the basal layer cannot be demonstrated by staining for CK5/6. (c) Final stage of urothelial differentiation with normal expression of CK20 limited to the umbrella cells and presence of normal basal layer manifesting expression of CK5/6.