As the seminal vesicles are often invaded by prostatic adenocarcinoma, the lack of PSA immunostaining in SVC is very useful differential diagnostic clue, but does not completely exclude anaplastic prostatic adenocarcinoma, which may be PSA negative.[5] SVC usually expresses CK7 but not CK 20. The gene discussed is KLK3; the disease is prostate adenocarcinoma.