CK7

CK7 (Cytokeratin 7) is a type II keratin protein produced by simple, non‑keratinising epithelial cells. It is encoded by the KRT7 gene, which is part of the keratin family responsible for forming the intermediate filament cytoskeleton inside epithelial cells. This cytoskeletal network helps maintain cell shape, mechanical strength, and structural stability. CK7 is normally expressed in simple, pseudostratified, and ductal epithelium, as well as mesothelium and urothelium. In a diagnostic setting CK7 is used because its expression pattern is positive in many epithelial cancers (such as lung, breast, thyroid, endometrium, cervix, ovary) and negative in others (such as colorectal or hepatocellular carcinoma). This helps identify the likely origin of a tumour, especially in metastatic disease (1).

Recommended Controls

Criteria for acceptable staining is a membranous and cytoplasmic staining pattern. The recommended controls to include are normal lung, normal bowel and/or appendix. The lung will demonstrate strong positive cytoplasmic and membranous staining of the alveolar cells and type II pneumocytes while the normal bowel will be negative. The appendix should not show any staining in the epithelial cells.

Expected staining pattern

Normal lung

Normal colon

Appendix mucosa

Disclaimer

These methods are intended as a guide only. Laboratories that wish to implement these methods should perform internal validation/verification prior to use. The RCPAQAP does not make any claim or warranty for the accuracy or performance of these methods.