Fig. 4

Representative images demonstrating the contribution of CK7/CK20 combination in different settings. A-C: Adenocarcinoma of the esophagus for which CK7/CK20 made no contribution to the diagnosis. This particular case was negative for both but other patterns would also be unhelpful in determining the origin of the tumor because of the variable CK7/CK20 staining patterns in esophageal adenocarcinoma (A: H&E; B: CK7; C: CK20). D-G: Lung adenocarcinoma where a pattern of CK7+/CK20- made a minor contribution to the diagnosis as this pattern is consistent with adenocarcinoma of the lung. However, there are more specific markers such as TTF1 (D: H&E; E: CK7; F:CK20; G: TTF1). H-I: Urothelial carcinoma in-situ for which CK20 staining made a major contribution to the diagnosis. This bladder biopsy shows a very thin urothelial layer where the cells show darkly stained nuclei, high N: C ratio and loss of polarity. The differential diagnoses include reactive changes, residual basal layer after sloughing of surface urothelial cells and urothelial carcinoma in-situ (clinging type). Strong and diffuse staining for CK20 supports the diagnosis of urothelial carcinoma in-situ (H: H&E; I: CK20)