KLK3 and breast cancer: Many of the most frequently determined cancer markers are characterized by low diagnostic sensitivity in the early stage of the disease, e.g., CA (carcinoma antigen) 15-3 breast cancer marker [26], CA19-9 pancreatic cancer marker [27], PSA (prostate-specific antigen) prostate cancer marker [28], and SCC-Ag (squamous cell carcinoma antigen) cervical cancer marker [29].