KLK3 and male reproductive organ cancer: Prostate-specific antigen (PSA) is the most commonly used screening tool for PCa in the clinic; however, not all patients with PCa have elevated PSA levels, and it is challenging to distinguish PCa from benign diseases, such as prostatitis and benign prostatic hyperplasia (BPH), by relying on PSA ≥ 4 ng/ml alone.