KLK3 and breast cancer: Several blood tumor markers are presently used for a wide range of cancer types including cancer antigen (CA)-125, α-fetoprotein (AFP), CA15-3/CA27.29 and prostate-specific antigen (PSA) for ovarian, liver, breast and prostate cancer, respectively, as well as β-2-microglobulin (B2M) for chronic lymphocytic leukemia, β-human chorionic gonadotropin (β-hCG) for testicular cancer; CA19-9 for gastric, gall bladder and pancreatic cancer; urokinase plasminogen activator (uPA) and plasminogen activator inhibitor (PAI-1) for breast cancer; and thyroglobulin for thyroid cancer [4,5].