In this retrospective study of 209 patients, we developed a simple model to calculate the probability of diagnosing clinically significant prostate cancer (csPC) at MRI–ultrasound fusion biopsy in men with low suspicion of the disease (prostate specific antigen < 10 ng/mL; normal digital rectal examination) but positive magnetic resonance imaging findings. The gene discussed is KLK3; the disease is prostate cancer.