Cytokeratins are intermediate-filament keratins found in the intracytoplasmic cytoskeleton of epithelial tissue. There are two types of cytokeratins: the low-weight, acidic Type I cytokeratins and the high-weight, basic or neutral Type II cytokeratins. Cytokeratins are usually found in pairs comprising a Type I cytokeratin and a Type II cytokeratin. Expression of these cytokeratins is frequently organ or tissue-specific. ^1-5

High molecular weight keratin antibody reacts with human keratin intermediate filament proteins 1, 5, 10 and 14. Expressed in squamous epithelium, ductal epithelium and other stratified epithelia. It is a specific marker for prostate basal cells and is often combined with p63 to show prostate basal cells to assist in the diagnosis of prostate, and can also be used to identify tumors of ductal and lobular epithelial origin in the breast.