If CDX2 and SATB2 are both negative, or if CK7 is positive but CK20 and TRPS1 are negative, third-tier immunostains including p63, GATA3, uroplakin II/III, PSA, and NKX3.1 should be performed to further classify the tumor as urothelial or prostatic secondary EMPD. The gene discussed is KLK3; the disease is extramammary Paget disease.