However, this might not be the case for some rare and special differential diagnostic considerations as for example in the discrimination of ductal prostate cancer and the enteric type of urachal adenocarcinomas, in which immunohistochemistry for prostate specific acid phosphatase (PAP) and prostate-specific antigen (PSA) (both negative in urachal adenocarcinomas and positive in ductal prostate cancer) might be useful [21, 27, 74, 77, 100, 245, 255, 357]. The gene discussed is KLK3; the disease is bladder urachal adenocarcinoma.