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. This evidence concerns the gene KLK3 and benign prostatic hyperplasia.