Cytokeratin 20 (CK20, K20)

Author: Kara Hamilton, M.S., Nat Pernick, M.D. (see Authors page)

Revised: 11 December 2015, last major update July 2013

Copyright: (c) 2003-2015,, Inc.

PubMed Search: CK20
Cite this page: Cytokeratin 20 (CK20, K20). website. Accessed February 23rd, 2018.
Definition / general
  • Epithelial marker (MW 46 kDa) with restricted expression compared to CK7 (OMIM #608218)
Uses by pathologists
Microscopic (histologic) images

Images hosted on Pathout server:

Merkel cell carcinoma; #3-FNA

Contributed by Leica Microsystems, Biosystems Division:

Colon (normal): cytokeratin 20
(PW31) with intense cytoplasmic

Images hosted on other servers:

Anal glands are CK20- (fig 1C) but rectal adenocarcinoma is CK20+ (fig 2)

Cervical adenocarcinoma: intestinal type is CK20- (fig 1E)

Colonic adenocarcinoma: #1-well differentiated; #2-poorly differentiated; #3-metastatic; #4-primary (fig G) and metastatic to lung (fig H)

Colonic medullary
carcinoma (fig 4)

Craniopharyngioma is CK20- (fig 1C); Rathke cleft cyst is CK20+ (fig 2C);
pituitary gland pars intermedia is CK20+ (fig 3C)

Gastric epithelium (normal)

Gastric carcinoma (poorly differentiated, fig 4A)

Merkel cell carcinoma; #3-FNA

Pancreatic ductal carcinoma is CK20- (fig 1F); adenocarcinoma of gallbladder is CK20+

PanIN lesions: CK20+ in grades 1, 2 and 3

Prostatic adenocarcinoma; #2 with positive staining of verumontanum

Rectal adenocarcinoma (fig 2)

Sinonasal adenocarcinoma: intestinal type (fig 4B)

Testicular mucinous cystadenoma is CK20+ (fig 3A), but ovarian tumor is CK20- (fig 5A)

Tubular adenocarcinoma

Urothelial carcinoma: #1-high grade; #2-CK20+ primary and nodal metastasis; #3 (CK20-, uncommon)

Images hosted on

Barretts: classic and non classic staining patterns

Intestinal metaplasia of the urinary bladder (fig C); typical cystitis glandularis (fig H)

Lung: nonmucinous bronchioloalveolar carcinoma is CK20- (fig 1D)

Lung: mucinous bronchioloalveolar carcinoma is CK20+ (fig 2D)

Pancreatic carcinoma (fig B, D and F)

Urothelium (normal, fig 1B)

Urothelial papilloma (fig 2C)

Urothelial papillary neoplasm of LMP (fig 3C)

Urothelial CIS is diffusely
CK20+ (fig B)

Urothelial carcinoma: #2-papillary-high grade (fig 5C); #3-papillary-low grade (fig 4C);

Positive staining - normal
Positive staining - not malignant
Positive staining - malignant
Negative staining