K6 protein is also a high molecular weight (predicted 60.3 kDa), basic type keratin known to be expressed by proliferating squamous epithelia and usually complexes with K16 . Three isoforms of K6 exist (K6a, K6b, and K6c) which are encoded by three distinct genes: KRT6A, KRT6B, and KRT6C [13, 14]. K6a is the most abundant, representing about 77% of all forms found in epithelia and shares at least 97.6% amino acid identity with other K6 proteins. K6a has been detected in subpopulations of luminal and ductal myoepithelial cells in human mammary glands . A high proliferative population of K6a positive cells has also been described in the prostate gland . There have been only a few studies which have investigated the expression of the K6c isoform in human tissues as until recently there was a lack of isoform-specific gene probes and antibodies.