KLK3 and prostate cancer: However, on comparing both prostate cancer groups, we observed a decrease in the serum PSA levels in the PCa+DM group than in the PCa-DM group. The paradoxically lower PSA levels in the PCa+DM group (22.38 vs 39.72 ng/mL) may reflect the suppressive effect of low testosterone on PSA expression rather than less aggressive disease.