CK5/6

IHCDB

PO

Diagnostic use

 In the breast

• Helps defines a basal-like subtype of invasive ductal carcinoma of the breast that is usually CK5/6+, ER-, PR-, HER2-, EGFR+ with poorer prognosis (Clin Cancer Res 2006;12:1533); associated with premenopausal African American women (JAMA 2006;295:2492), BRCA1 (J Natl Cancer Inst 2003;95:1482, Mod Pathol 2005;18:1321) and brain metastases (Am J Surg Pathol 2006;30:1097)
• Defines a DCIS subtype with poorer prognosis (Hum Pathol 2007;38:197)
• Distinguish breast usual ductal hyperplasia (strong + staining) from solid papillary DCIS (negative, Hum Pathol 2006;37:787)

 SSC

• p63+ and CK5/6+ poorly differentiated metastatic carcinomas are likely to have squamous carcinoma primaries (Am J Clin Pathol 2001;116:823)

 cutaneous SCC

• Distinguish cutaneous spindled squamous cell carcinoma (CK5/6+ in 100%) from superficial epithelioid sarcoma (rare focal positivity, J Cutan Pathol 2003;30:114)

 mesothelioma

• Distinguish epithelioid mesothelioma (CK5/6+ cytoplasmic staining with perinuclear enhancement) from lung adenocarcinoma (usually CK5/6 negative, Histopathology 2006;48:223); also in pleural effusions (Diagn Cytopathol 2006;34:801)

References

 Subclassification of non-small cell lung carcinomas lacking morphologic differentiation on biopsy specimens: Utility of an immunohistochemical panel containing TTF-1, napsin A, p63, and CK5/6. Mukhopadhyay S, Katzenstein AL. Am J Surg Pathol. 2011 Jan;35(1):15-25. PMID: 21164283