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Table of Contents
Definition / general | Uses by pathologists | Positive staining - normal | Positive staining - disease | Microscopic (histologic) images | Additional referencesCite this page: Cytokeratin 6 (CK6, K6). PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/stainsck6.html. Accessed July 12th, 2017.
Definition / general
- Molecular weight is 56 kDa; major isoform is 6A
- Related to cytokeratin 5
- Paired with CK16 and CK17
- Mutations cause pachyonychia congenita (Ann N Y Acad Sci 2006;1082:56)
- Upregulated in conjunctiva in Sjogren's syndrome (Exp Eye Res 2003;77:17) and in cornea in keratoconus (Invest Ophthalmol Vis Sci 2003;44:2466)
- Marker of hyperproliferative and activated keratinocytes found in psoriasis (Dermatology 2000;201:15), wound healing and other inflammatory disorders (J Invest Dermatol 2001;116:330)
Uses by pathologists
- 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) 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)
- p63+ and CK5/6+ poorly differentiated metastatic carcinomas are likely to have squamous carcinoma primaries (Am J Clin Pathol 2001;116:823)
- 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)
- Distinguish cutaneous spindled squamous cell carcinoma (CK5/6+ in 100%) from superficial epithelioid sarcoma (rare focal positivity, J Cutan Pathol 2003;30:114)
Positive staining - normal
- Esophagus, epidermal and epithelial glands, hair and nails, oral mucosa, stomach, tongue (filiform papillae)
Positive staining - disease
- Psoriasis, other skin disorders (see above)
Microscopic (histologic) images
Images hosted on other servers:
Breast carcinoma-basal subtype in BRCA1 patient
Gallbladder adenosquamous carcinoma
Keratoconus (fig A), normal cornea (fig D)
Mesothelioma-deciduoid (fig 5)
Squamous cell carcinoma-oral (fig a)
Benign epithelial inclusions of axillary lymph nodes - fig 1: CK5/6+; 2: p63+
Images hosted on Nature.com:
Ovarian serous carcinoma (fig b)
Pancreas-adenosquamous carcinoma
Skin-various images
Various images #1 (squamous cell-fig 1A, urothelial-fig 1C, thymoma-fig 1E, salivary gland adenoid cystic-fig 1G)
#2 (ovary-fig 2A, endometrioid adenocarcinoma of uterus-fig 2C, infiltrating ductal carcinoma of breast-fig 2E)
Additional references
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