Participants in the German Familial Prostate Cancer database diagnosed from 1994 to 2019 with (1) low risk (clinical T1c–T2a, biopsy Gleason Grade Group (GGG) 1, PSA < 10 ng/ml), (2) Gleason 6 FIR (clinical T1c–T2a, GGG 1, PSA 10–20 ng/ml), and (3) Gleason 3 + 4 FIR (clinical T1c–T2a, GGG 2, PSA < 10 ng/ml) PCa who were subsequently treated with radical prostatectomy (RP) were analysed for upgrading, defined as postoperative GGG 3 tumour or upstaging, defined as pT3–pT4 or pN1 disease at RP. This evidence concerns the gene KLK3 and prostate cancer.