Revisiting the Use of CK7 and CK20 Immunohistochemical Stains in Pathological Diagnoses

Abstract Background: Cytokeratin-7 (keratin-7; CK7) and cytokeratin-20 (keratin-20; CK20) have been among the most widely used markers in pathology for prediction of tumor site of origin or classification. However, with the increased availability of newer and more specific biomarkers and molecular techniques, it is timely to revisit the utility of CK7 and CK20 stains under different clinical settings. Methods: In the current study, we retrospectively reviewed 612 surgical pathology cases at our institution where CK7 and/or CK20 stains were performed and determined to what degree they contributed to the final diagnosis. Results: In CK7-and-CK20 cases, the stains had a major contribution in 5% of the cases. In CK7-only or CK20-only cases, the percentages of major contribution were 34% and 69% respectively. However, when only cases where CK7/CK20 stains were used to determine tumor site of origin, the contributions become more comparable across all three case types, where CK7/CK20 stains had major contribution in < 10% of cases. Notably, 11% of CK7-and-CK20 cases had no specific or suggestive diagnosis, and 40% of CK7-and-CK20 cases had staining patterns inconsistent with the final diagnosis. Detailed analysis demonstrates that CK7 and CK20 stains, used singly, are most useful in the diagnosis of a limited number of pathologic entities with distinct CK7 or CK20 expression patterns. Conclusions: Our results suggest that the coordinate expression of CK7 and CK20 is generally not helpful in arriving at the final diagnosis. Reducing unnecessary immunohistochemical stains will help mitigate the rising healthcare cost and preserve tissue for molecular testing.