Test Catalog

Test ID: CTSK    
Cathepsin K Immunostain, Technical Component Only

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

A marker of myeloid lineage

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

·        Cathepsin K is a protease whose expression is driven by microphthalmia transcription factor (MITF) in osteoclasts. Cathepsin K is also expressed in renal perivascular epithelioid cell neoplasms (PEComas), alveolar soft part sarcoma, and most MiT family translocation -renal cell carcinomas. This includes most transcription factor EB- (TFEB) rearranged renal cell carcinomas, those with amplifications of TFEB, and renal cell carcinomas that harbor various TFE3 gene fusions.

Interpretation Provides information to assist in interpretation of the test results

This test does not include pathologist interpretation; only technical performance of the stain. If interpretation is required order PATHC / Pathology Consultation for a full diagnostic evaluation or second opinion of the case.

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. Martignoni G, Bonetti F, Chilosi M, et al: Cathepsin K expression in the spectrum of perivascular epithelioid cell (PEC) lesions of the kidney. Mod Pathol. 2012;25(1):100-111. doi: 10.1038/modpathol.2011.136

2. Rao Q, Cheng L, Xia QY, et al: Cathepsin K expression in a wide spectrum of pervascular epithelioid cell neoplasms (PEComas): a clinicopathological study emphasizing external PEComas. Histol. 2013;62(4):642-650. doi: 10.1111/his.12059

3. Martignoni G, Gobbo S, Camparo P, et al: Differential expression of cathepsin K in neoplasms harboring TFE3 gene fusions. Mod Pathol. 2011;24(10):1313-1319. doi: 10.1038/modpathol.2011.93

4. Rao Q, Wang Y, Xia Q, et al: Cathepsin K in the immunohistochemical diagnosis of melanocytic lesions. Int J Clin Exp Pathol. 2014;7(3):1132-1139