Cytokeratineexpressionpatronen

Cytokeratineexpressionpatronen, or cytokeratin expression patterns, describe the characteristic set of cytokeratin proteins detected in an epithelial cell or tumor. They are determined by immunohistochemical staining and reflect the differentiation state and tissue origin of the epithelium. Analyzing these patterns helps pathologists classify tumors and infer their primary site when metastases are involved.

Cytokeratins are intermediate filament proteins in epithelial cells, encoded by KRT genes. They are divided into type I (acidic) and type II (basic to neutral) subfamilies and form heterodimers that assemble into filaments. Different epithelial tissues express distinct repertoires of cytokeratins; commonly used markers include CK7, CK8/18, CK19 (typical of simple epithelia), CK5/6 and CK14 (basal/stratified epithelia), and CK20 (gastrointestinal and urothelial epithelia). The combination of positive CKs, rather than a single marker, defines a cytokeratin expression pattern characteristic of a lineage or differentiation state.

Common patterns and interpretive examples: CK7+/CK20- is typical of many carcinomas of lung, breast, and ovary, whereas CK7-/CK20+ favors colorectal carcinoma. CK20 positivity with CK7 negativity is often seen in Merkel cell carcinoma. Pan-cytokeratin antibodies (AE1/AE3) stain most epithelial tumors, but some carcinomas may be CK-negative or variably expressed, especially when poorly differentiated.

Applications and limitations: Cytokeratin expression patterns are integral to immunohistochemical workups, supporting tumor typing, detecting metastatic disease, and guiding therapy. Limitations include variable expression in poorly differentiated tumors, overlap among tumor types, and the need to interpret results with morphology and clinical history.