The most common identities used for cancer diagnosis are cancer antigen 125 (CA125), α-fetoprotein (AFP), cancer antigen 19-9 (CA19-9), cancer antigen 153 (CA15-3), carcinoembryonic antigen (CEA), epidermal growth factor receptor (EGFR), breast cancer (BRCA), prostate-specific antigen (PSA), interleukins (ILs), mucin 1 (MUC 1), tumor necrosis factor-alpha (TNF-α), human epidermal growth factor receptor 2 (HER2), vascular endothelial growth factor (VEGF) and squamous cell carcinoma antigen (SCC-Ag). This evidence concerns the gene KLK3 and breast cancer.