In a comprehensive analysis, Larkin et al. utilized isobaric stable isotope labeling (iTRAQ) in conjunction with liquid chromatography–tandem mass spectrometry (LC-MS/MS) to investigate whole, non-depleted serum from various groups, including controls (PSA < 1 ng/mL), benign prostate diseases (such as prostatitis and BPH), early-stage (T1-T2) prostate cancer, and late-stage (T3-T4) cancer [38]. Here, KLK3 is linked to cancer.