Test Catalog

Test ID: KRT7    
Keratin 7 (KRT7) Immunostain, Technical Component Only

Useful For Suggests clinical disorders or settings where the test may be helpful

Aiding in determining the primary site in carcinomas of unknown origin

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

For the initial technical component only immunohistochemical (IHC) stain performed, the appropriate bill-only test ID will be reflexed and charged (IHTOI). For each additional technical component only IHC stain performed, an additional bill-only test ID will be reflexed and charged (IHTOA).

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Keratin 7 (KRT7) stains the cytoplasm of epithelial cells in a granular and/or filamentous pattern, or may appear membrane associated (cytoskeletal). In normal tissues, KRT7 is found in a large number of cell types including many ductal and glandular epithelia (biliary and pancreatic ducts, lung alveoli, breast, ovary, endometrium, renal collecting ducts, urothelium, thyroid, placental trophoblasts, and mesothelium). When used together, KRT7 and KRT20 may be useful as an aid in determining the primary site in carcinomas of unknown origin.

Interpretation Provides information to assist in interpretation of the test results

This test includes only technical performance of the stain (no pathologist interpretation is performed). Mayo Clinic cannot provide an interpretation of tech only stains outside the context of a pathology consultation. If an interpretation is needed, refer to PATHC / Pathology Consultation for a full diagnostic evaluation or second opinion of the case. All material associated with the case is required. Additional specific stains may be requested as part of the pathology consultation, and will be performed as necessary at the discretion of the Mayo pathologist.


The positive and negative controls are verified as showing appropriate immunoreactivity and documentation is retained at Mayo Clinic Rochester. If a control tissue is not included on the slide, a scanned image of the relevant quality control tissue is available upon request. Contact 855-516-8404.


Interpretation of this test should be performed in the context of the patient's clinical history and other diagnostic tests by a qualified pathologist.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Age of a cut paraffin section can affect immunoreactivity. Stability thresholds vary widely among published literature and are antigen-dependent. Best practice is for paraffin sections to be cut within 6 weeks.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Bayrak R, Haltas H, Yenidunya S: The value of CDX2 and cytokeratins 7 and 20 expression in differentiating colorectal adenocarcinomas from extraintestinal gastrointestinal adenocarcinomas: cytokeratin 7-/20+ phenotype is more specific than CDX2 antibody. Diagn Pathol 2012;7:9-19

2. Campbell F, Herrington CS: Application of cytokeratin 7 and 20 immunohistochemistry to diagnostic pathology. Curr Diagn Pathol 2001;7:113-122

3.  Jin L, Liu Y, et al: Immunohistochemical analysis and comparison of Napsin A, TTF1, SPA and CK7 expression in primary lung adenocarcinoma. Biotech Histochem 2018;93(5):364-372