Cytokeratin 5 (58 kDa) is a high-molecular-weight, basic type of cytokeratin that is expressed in various layers of stratified epithelia, including the basal, intermediate, and superficial-cell layers. It is also found in transitional epithelia, complex epithelia, mesothelial cells, and mesothelioma. On the other hand, cytokeratin 6 (56 kDa) is another high-molecular-weight, basic type cytokeratin that is often expressed in proliferating squamous epithelium and is frequently co-expressed with cytokeratin 16.

The Cytokeratin 5 & 6 antibody can be used to detect the presence of these proteins. It is highly positive in nearly 100% of malignant mesotheliomas, a type of cancer that originates from the mesothelial cells lining the pleura, peritoneum, or pericardium. However, it is rarely observed in lung adenocarcinomas. The antibody can also be positive in undifferentiated large-cell carcinomas and squamous carcinomas. In contrast, fewer than 10% of breast, colon, and prostate carcinomas show positivity for this marker.

Furthermore, the Cytokeratin 5 & 6 antibody has been successfully employed as a myoepithelial cell marker in the prostate to determine malignancy. Myoepithelial cells are specialized cells that surround the epithelial cells in various tissues, including the prostate gland.