Cytokeratin 19 (CK19, K19)

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

Revised: 2 December 2016, last major update October 2013

Copyright: (c) 2003-2016,, Inc.

PubMed Search: CK19[title]
Cite this page: Cytokeratin 19 (CK19, K19). website. Accessed March 24th, 2018.
Definition / general
  • Molecular weight is 40 kDa (smallest cytokeratin)
  • Often coexpressed with CK7
  • Present in both simple and complex epithelium
  • Involved in the organization of myofibers; links contractile apparatus to dystrophin at costameres of striated muscle (also CK8, Mol Biol Cell 2005;16:4280)
  • Polymorphisms of CK19 pseudogene are associated with primary biliary cirrhosis (Hepatol Res 2003;25:281)
Uses by pathologists
  1. Bladder: possible urine screening test for bladder carcinoma (J Egypt Natl Canc Inst 2006;18:82)
  2. Bone / soft tissue: distinguish chordoma (CK19+) from parachordoma (CK19-, Ann Diagn Pathol 1997;1:3)
  3. Breast: presence of CK19+ peripheral blood tumor cells or CK19+ fragments is a poor prognostic factor for breast cancer (predicts CNS relapse, Breast Cancer Res 2006;8:R36)
  4. Liver: distinguish hepatocellular carcinoma (CK19-) from either hepatoid adenocarcinoma metastatic to liver (CK19+, Am J Surg Pathol 2003;27:1302) or cholangiocarcinoma (CK19+, J Gastrointestin Liver Dis 2006;15:9, Am J Clin Pathol 2006;125:519)
  5. Liver: poor prognostic factor in hepatocellular carcinoma (Histopathology 2006;49:138, Cancer Sci 2003;94:851)
  6. Lung: poor prognostic factor for non small cell lung carcinoma (Ann N Y Acad Sci 2006;1075:244, Cancer 2006;107:2842)
  7. Pancreas: poor prognostic factor in pancreatic endocrine neoplasms (Am J Surg Pathol 2004;28:1145, Am J Surg Pathol 2006;30:1588)
  8. Thyroid: confirm diagnosis of papillary thyroid carcinoma in cytology or equivocal cases (Arch Pathol Lab Med 2003;127:579, Mod Pathol 2006;19:1631); help distinguish follicular variant of papillary thyroid carcinoma (CK19+) from (a) follicular adenoma (CK19-, Endocr Pathol 2006;17:213, Am J Clin Pathol 2006;126:700 but see Am J Clin Pathol 2001;116:696), (b) hyalinizing trabecular adenoma (CK19-, Am J Surg Pathol 2006;30:1269), (c) Grave’s disease (weak / negative CK19, Endocr Pathol 2005;16:63), (d) multinodular goiter with papillary areas (Endocr Pathol 2002;13:207); note that CK19 may stain benign thyroid lesions
  9. Metastases: RT-PCR detects nodal and marrow metastases in various carcinomas - bladder carcinoma (poorer survival, Clin Cancer Res 2005;11:3773), breast (Anticancer Res 2006;26:3855, Jpn J Clin Oncol 2003;33:167), gastric (World J Gastroenterol 2006;12:5219), head and neck squamous cell (Br J Cancer 2006;94:1164), skin (Br J Dermatol 2003;149:998); note that pelvic lymph nodes may have false positives (Int J Cancer 2007;120:1842)
  10. Peripheral blood tumor cells: RT-PCR detects peripheral blood tumor cells in carcinoma of cervix (Gynecol Oncol 2002;85:148), colon (Gut 2002;50:530), gallbladder (Rev Med Chil 2004;132:1489), pancreas (World J Gastroenterol 2007;13:257); the significance of these tumor cells is unclear (Ann Oncol 2005;16:1845)
Positive staining - normal
Positive staining - not malignant
Positive staining - malignant
Negative stains
Microscopic (histologic) images
Images hosted on PathOut server:

Courtesy of Andrey Bychkov, M.D., Ph.D.

CK19: clear de-
marcation between
cancer tissue
and thyroid

CK19: prominent membranous and cytoplasmic staining

Images hosted on other servers:

Clear cell odontogenic carcinoma (fig 7B)

Pancreatic ductal carcinoma (fig D)

Squamous cell carcinoma - oral (fig B)

Stomach - complete intestinal metaplasia

Thyroid lesions - various

Images hosted on

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Endolymphatic sac tumor

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Renal low grade tubularmucinous neoplasm

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Thyroid papillary carcinoma

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Follicular variant (fig D)

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Thyroid nodular goiter has focal CK19+ (fig I)

Additional references