KLK3 and breast cancer: Prostate-specific antigen (PSA) is one of the common protein biomarkers assessed in the clinical identification of prostate cancer (Tkac et al., 2019), Similarly, cancer antigen 125 (CA 125) level is checked for ovarian cancer (Romeo and Seropian, 2021), alpha-fetoprotein (AFP) level is checked for liver cancer (Zhang et al., 2018), CA19.9 level is checked for gastric/pancreatic cancer (Subki et al., 2021), carcinoembryonic antigen (CEA) level is checked for colorectal cancer (Zhao et al., 2018), and cancer antigen 15.3 (CA15.3)/CA27.29 level is checked for breast cancer (Li et al., 2018).