Cytokeratin 7 (CK7, K7)

Author: Brandon Umphress, M.D. and Kruti P. Maniar, M.D.

Revised: 23 July 2018, last major update June 2018

Copyright: (c) 2003-2018,, Inc.

PubMed Search: CK7 stain "loattrfree full text"[sb]
Cite this page: Umphress, B., Maniar, K.P. Cytokeratin 7 (CK7, K7). website. Accessed August 17th, 2018.
Definition / general
  • Type II keratin of simple nonkeratinizing epithelia (OMIM: 148059 [Accessed 21 June 2018]); molecular weight 51.4 kDa
  • Expression similar to but more limited than keratins 8 and 18 in simple, pseudostratified and ductal epithelium; mesothelium; 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 adenocarcinoma
  • 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; 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
  • Membranous / cytoplasmic staining, ranging from weak / focal to strong / diffuse
Microscopic (histologic) images

Scroll to see all 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

 Contributed by
 Dr. Semir Vranic,
 University of Sarajevo
 (Bosnia and Herzegovina)

Ampullary adenocarcinoma

 Case of the Week

Breast metaplastic carcinoma

Case of the Week

Cardiac myxoma with glandular differentiation

 Case of the Week

Lung adenocarcinoma: metastatic to ovary

 Case of the Week

Nasal cavity: seromucinous hamartoma

Case of the Week

Prostate: left nephrogenic adenoma

 Case of the Week

Urethra: clear cell adenocarcinoma

 Contributed by
 Leica Microsystems,
 (Biosystems Division)

Ureter (normal)
CK7 (RN7) with
intense cytoplasmic

Images hosted on other servers:

Anal glands (left-fig E) and transitional zone (right, fig 1B) are CK7+

Anal gland carcinoma is CK7+ (fig C)

Bladder: carcinoid and urothelium are CK7+ (fig F)

Bladder mucinous cystadenocarcinoma

Bladder / urethra: clear cell adenocarcinoma

Breast: Left-cylindroma; right-Paget disease

Cervical adenocarcinoma: Left-intestinal type (fig C); right-signet ring type (fig C)

extrahepatic (fig C)
and gallbladder (fig A)

Colonic and lung carcinoma (fig D-F)

Kidney: left - chromophobe carcinoma-eosinophilic variant is CK7+ (fig 2C); right - oncocytoma has scattered CK7+ cells (fig 6)

Nasal cavity: inverted papilloma


Ovarian mucinous cystadenoma is CK7+
(5B) but testicular mucinous cystadenoma
(fig 3B) and colonic epithelium (fig 4B)
are negative

Pancreas: ductal adenocarcinoma (fig E)

Penis / scrotum: mucoid cyst (Fig 6)

Urothelial carcinoma:
with glandular
differentiation (fig 4)

 Images hosted on Flickr:
Missing Image

Nasal cavity:
respiratory epithelial

Positive staining - malignant
Negative staining - normal
Board review question #1
54 year old woman presents with a 10 cm right ovarian mass. Histology demonstrates a mucinous carcinoma and immunohistochemical stains demonstrate the tumor cells to be 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- (although lower GI type mucinous tumors arising in teratoma can be CK7-).