Stains & molecular markers
Cytokeratin 7 (CK7, K7)

Topic Completed: 1 June 2018

Minor changes: 2 June 2020

Copyright: 2003-2020,, Inc.

PubMed Search: CK7 stain "loattrfree full text"[sb]

Kruti P. Maniar, M.D.
Brandon Umphress, M.D.
Page views in 2019: 56,198
Page views in 2020 to date: 31,239
Cite this page: Maniar KP, Umphress B. Cytokeratin 7 (CK7, K7). website. Accessed July 8th, 2020.
Definition / general
  • Type II keratin of simple nonkeratinizing epithelia; molecular weight 51.4 kDa (OMIM: 148059 [Accessed 14 September 2018])
  • Expression similar to but more limited than keratins 8 and 18 in simple, pseudostratified and ductal epithelium, mesothelium and urothelium
Essential features
  • Membranous / cytoplasmic marker with expression in many normal epithelia and epithelial tumors
  • Despite wide distribution, useful as part of a panel in determining primary site of metastatic carcinoma
  • Generally expressed (with some variation) in adenocarcinoma of lung, breast, thyroid, endometrium, cervix, ovary, salivary gland and upper GI tract, urothelial carcinoma, papillary renal cell carcinoma and Paget disease
  • Generally negative (with some variation) in colorectal carcinoma, Merkel cell carcinoma, hepatocellular carcinoma, prostatic adenocarcinoma, adrenocortical tumors and squamous cell carcinoma
  • Also known as keratin 7, CK7, KRT 7, K7
  • Like other keratins, component of intermediate filaments forming cytoskeleton of epithelial cells (J Anat 2009;214:516)
  • Type II keratins, arranged in pairs of heterotypic keratin chains, are expressed during differentiation of certain epithelial tissues (NCBI - Gene - KRT7)
Uses by pathologists
Prognostic factors
  • CK7 expression in esophageal squamous cell carcinoma is an independent prognostic factor for poor overall survival (Neoplasma 2018;65:469)
  • CK7 / CK19 index is an independent adverse prognostic factor for postoperative survival in intrahepatic cholangiocarcinoma patients (J Surg Oncol 2018;117:1531)
  • No association with prognosis when used as a marker for intestinal versus pancreaticobiliaryorigin in ampullary carcinoma (Am J Surg Pathol 2017;41:865)
  • Expression in cervical low grade squamous intraepithelial lesion (LSIL / CIN 1) associated with higher rates of subsequent HSIL but clinical utility potentially limited by low magnitude of risk difference and interpretive variability; no prognostic utility in CIN 2 (Am J Surg Pathol 2013;37:1311, Am J Surg Pathol 2017;41:143, Am J Surg Pathol 2018;42:479)
  • Membranous / cytoplasmic staining, ranging from weak / focal to strong / diffuse
Microscopic (histologic) images

Contributed by Kruti P. Maniar, M.D.

Cervical squamocolumnar junction

Cholangio- carcinoma


Liver portal tract

Lung adenocarcinoma

Ovarian seromucinous borderline tumor


Yolk sac tumor, glandular variant

Contributed by
Andrey Bychkov, M.D., Ph.D.

Ovarian cancer

Urothelial carcinoma

 Case of the Week

Urethra: clear cell adenocarcinoma

 Contributed by
 Leica Microsystems,
 (Biosystems Division)

Ureter (normal)

Positive staining - malignant
Negative staining - normal
Board review style question #1
A 54 year old woman presents with a 10 cm right ovarian mass. Histology demonstrates a mucinous carcinoma and the tumor cells are negative for CK7 and positive for CK20. Which of the following tumors is most likely to demonstrate this immunohistochemical profile?

  1. Metastatic breast adenocarcinoma
  2. Metastatic cervical adenocarcinoma
  3. Metastatic colonic adenocarcinoma
  4. Metastatic gastric adenocarcinoma
  5. Primary ovarian mucinous carcinoma
Board review answer #1
C. Adenocarcinoma of the colon is most often CK7- / CK20+. Breast carcinoma is usually CK7+ / CK20-, cervical adenocarcinoma is usually CK7+ / CK20-, gastric carcinoma can be either CK7+ / CK20- (majority) or CK7+ / CK20+ and primary ovarian mucinous carcinoma is either CK7+ / CK20+ or CK7+ / CK20 variable (although lower GI type mucinous tumors arising in teratoma can be CK7-).
Back to top