Cytokeratin 20

This cytokeratin is distantly related to other acidic (type I) keratins. It was formerly known as "protein IT".

Reliable demonstration in paraffin sections requires antigen retrieval by pressure cooking.

Immunohistochemical expression

This cytokeratin is expressed by:

•  Gastrointestinal epithelium and gastrointestinal carcinomas

• Urothelium and transitional cell carcinomas: usually CK7+/CK20+

• Colorectal carcinoma

• Gastric carcinoma, less reliably positive

• Some adenocarcinomas of the biliary tree and pancreatic duct

• Mucinous ovarian adenocarcinoma

• Rarely in islet cell tumours: 1/7 cases3

• Transitional cell carcinoma: 24/33 cases3, 13/19 pure transitional cell carcinomas6, 16/19 transitional cell carcinomas with focal squamous metaplasia6.

• Merkel cell carcinoma (punctate globular inclusion-like or perinuclear pattern of staining)

• Small cell carcinoma of the salivary gland

• Small intestinal carcinoids; 6/7 cases3

• Prostate: 10/36 cases3

• Some mesothliomas: 18/407

Generally not expressed by:

• Small cell carcinomas, other than those of the salivary gland and Merkel cell tumours

• Squamous cell carcinomas of the

  • lung: 0/39 cases3, 0/11(metastases to cervical nodes)11
    
  • larynx: 0/32 cases3
    
  • bladder: 0/4 cases6
    
  • uterine cervix: 0/17 cases3

• Thyroid tumours:

  • follicular adenoma: 0/17 cases3

  • follicular carcinoma: 0/10 cases3

  • papillary carcinoma: 0/30 cases3

• Seminoma: 0/30 cases3

• Thymoma: 0/29 cases 3

Where the subject has been examined, there is concordance in the expression of cytokeratin 20 between primary carcinomas and their lymph node metastases.5

Diagnostic utility

• The coordinate expression of cytokeratins 7 and 20 is particularly useful in identifying the primary site of a carcinoma.

• It is useful in the differential diagnosis of small cell carcinomas:

References

Chan JKC et al.  Cytokeratin 20 immunoreactivity distinguishes Merkel cell (primary cutaneous neuroendocrine) carcinomas and salivary gland small cell carcinomas from small cell carcinomas of various sites.  Am J Surg Pathol 1997;21:226-34

Adv Anat Pathol 1997;4:261-2.

3 Miettinen M. Keratin 20: immunohistochemical marker for gastrointestinal, urothelial and Merkel cell carcinomas. Mod Pathol 1995;8:384-388.

4 Cheuk W et al. Immunostaining for thyroid transcription factor-1 and cytokeratin 20 aids in the distinction of small cell carcinoma from Merkel cell carcinoma, but not pulmonary from extrapulmonary small cell carcinoma. Arch Pathol Lab Med 2001;125:228-231.

5 Jiang et al. Cytokeratin 7 and cytokeratin 20 in primary urinary bladder carcinoma and matched lymph node metastasis. Arch Pathol Lab Med 2001;125:921-3.

6 Harnden, P., Southgate, J. Cytokeratin 14 as a marker of squamous differentiation in transitional cell carcinomasJ Clin Pathol 1997;50:1032-3.

7 Garcia-Prats, M. D., C. Ballestin, et al. (1998). "A comparative evaluation of immunohistochemical markers for the differential diagnosis of malignant pleural tumours." Histopathology 32(5): 462-72.

8 Jerome Marson, V., J. Mazieres, et al. (2004). "Expression of TTF-1 and cytokeratins in primary and secondary epithelial lung tumours: correlation with histological type and grade." Histopathology 45(2): 125-34.

9 Kaufmann, O., T. Deidesheimer, et al. (1996). "Immunohistochemical differentiation of metastatic breast carcinomas from metastatic adenocarcinomas of other common primary sites." Histopathology 29(3): 233-40.

10 Lagendijk, J. H., H. Mullink, et al. (1999). "Immunohistochemical differentiation between primary adenocarcinomas of the ovary and ovarian metastases of colonic and breast origin. Comparison between a statistical and an intuitive approach." J Clin Pathol 52(4): 283-90.

11 Roh MS,Hong SH Utility of thyroid transcription factor-1 and cytokeratin 20 in identifying the origin of metastatic carcinomas of cervical lymph nodes. J Korean Med Sci 2002; 17:512-7 FULL TEXT

12 Dennis JL, Hvidsten TR, Wit EC, et al. Markers of adenocarcinoma characteristic of the site of origin: development of a diagnostic algorithm. Clin Cancer Res 2005; 11:3766-72 FULL TEXT

©SMUHT/PW Bishop