KLK3 and male reproductive organ cancer: From these early PSA studies, it was not believed that PSA could be used as a screening tool for PCa; until the early 1990s, it was primarily used for monitoring treatment response in patients who already had an established PCa diagnosis [2,5], and it was already known that patients with other prostatic diseases, such as benign prostatic hyperplasia (BPH) and prostatitis, could also present higher PSA levels.