Prostein (also known as prostate cancer-associated protein 6 / P501S / SLC45A3) is a protein present in the Golgi apparatus of benign and malignant prostatic glandular epithelium. Because it is highly specific for prostate glandular cells, this target is useful for differentiating extra-prostatic metastases from other carcinomas such as urothelial carcinomas or colorectal carcinomas. Although it may show diminished expression in some aggressive prostate cancers, this target is sometimes expressed in PSA-negative prostate carcinomas, and these two targets used in combination can lead to increased sensitivity in the identification of prostate cancer metastases. Prostein is expected to have perinuclear cytoplasmic staining in prostate tissue. References: Xu, 2001; Sheridan, 2007; Lane, 2008; Chuang, 2007; Sheridan, 2007 Perner, 2013