Cytokeratins are intermediate filaments present in all epithelial cells, and also in a number of non-epithelial cells. In fact, cytokeratin positively has been reported in almost every tumour type, including uterine smooth muscle tumours, most soft tissue sarcomas, melanomas, gliomas, plasmacytomas and occasionally lymphomas.


 They form two group:


  I: acidic cytokeratins, assigned Moll numbers 9 to 20


  II: basic cytokeratins, assigned Moll numbers 1 to 8


Each type I cytokeratin forms a pair with a type II cytokeratin and all epithelial cells contain at least two cytokeratins. The exception is cytokeratin 19, which exists in an unpaired state. The type I cytokeratin usually pairs with a type II cytokeratin which is 7 to 9 kD larger.2

Cytokeratins may also be classified as low molecular weight (commonly 8, 18 and 19) and high molecular weight (commonly 1, 5, 10 and 14).


Diagnostic utility


1Southgate, J., Harnden, P., Trejdosiewicz, L. K. Cytokeratin expression patterns in normal and malignant urothelium: a review of the biological and diagnostic implications. Histol Histopathol 1999;14:657-664.

2Diagnostic Immunohistochemistry edited by Professor D. J. Dabbs, page 60.

3Dargent, J. L., Jochmans, K., De Waele, M., Schots, R., Bourgain, C. Cytokeratin expression by CD34 positive blasts in a case of refractory anaemia with excess of blasts in transformation (RAEB-t). J Clin Pathol 2001;54:735.

©SMUHT/PW Bishop