The ectopic expression of PSA has been reported in smaller concentrations in the tissue of malignant breast tumors (10), normal breast tissue (11,12), breast milk (13), female serum (12), and adrenal and renal carcinomas (14); however, for practical and clinical purposes, PSA is organ-specific and is primarily produced by prostatic luminal epithelial cells (13,15,16). The gene discussed is KLK3; the disease is breast cancer.