KLK3 and prostate cancer: In the absence of other clinical parameters of improved outcome in patients with prostate cancer, the Prostate Cancer Clinical Trials Working Group 2 determined that the percentage decline in prostate-specific antigen (PSA) from baseline to 12 weeks (or earlier for those who discontinue therapy), as well as the maximum decline in PSA that occurs at any point after treatment, be reported as a surrogate marker for favourable response [7].