Gleason scores, particularly when used in combination with other clinical factors, including PSA level and clinical tumor stage, are the strongest markers of prostate cancer prognosis and progression currently available (D’Amico et al., 1998; Montironi et al., 2005; Cooperberg et al., 2009; Chang et al., 2014; Epstein et al., 2016). The gene discussed is KLK3; the disease is prostate cancer.