KRT20 and extramammary Paget disease: CK20 is usually negative in primary EMPD, so it can be used to discern the primary from the secondary EMPD, such as originating from colorectal cancer; in our cohort, about 5% of cases expressed variable CK20, which suggested that, in practice, we should use a panel marker including CK20 and other biomarkers to make differential diagnosis.