Test Catalog

Test ID: KRT5    
Keratin 5 (KRT5) Immunostain, Technical Component Only

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

Differentiation of mesothelioma and squamous cell carcinoma versus adenocarcinoma

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 5 is a type II cytokeratin that dimerizes with the type I cytokeratin 14 forming intermediate filaments in the basal layer of the epidermis. Squamous epithelium of normal skin stains in a cytoplasmic pattern with keratin 5. Keratin 5 is usually positive in mesotheliomas and negative in adenocarcinomas, making it useful in separating mesotheliomas from pulmonary adenocarcinomas.

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. Boecker W, Stenman G, Loening T, et al: Squamous/epidermoid differentiation in normal breast and salivary gland tissues and their corresponding tumors originate from p63/K5/14-positive progenitor cells. Virchows Arch 2015;466(1):21-36

2. Chu PG, Weiss LM: Expression of Cytokeratin 5/6 in Epithelial Neoplasms: an Immunohistochemical Study of 509 Cases. Mod Pathol 2002;15(1):6-10

3. Kaufmann O, Fietze E, Mengs J, Dietel M: Value of p63 and Cytokeratin 5/6 as Immunohistochemical Markers for the Differential Diagnosis of Poorly Differentiated and Undifferentiated Carcinomas. Am J Clin Pathol 2001;116(6):823-830

4. Miettinen M, Sarlomo-Rikala M: Expression of calretinin, thrombomodulin, keratin 5, and mesothelin in lung carcinomas of different types: an immunohistochemical analysis of 596 tumors in comparison with epithelioid mesotheliomas of the pleura. Am J Surg Pathol 2003;27(2):150-158