KLK3 and Familial prostate cancer: However, the low PSA level does not necessarily mean a “clinical insignificance.” In the study of Walz et al., the incidence rates of prostate cancer in men with PSA < or = 2.5 ng/mL were 16.5% and 36.5%, if these patients had a pT3 stage and Gleason score, respectively, [100].