PROS1 and cancer: To improve on the Gleason system, additional clinical factors, most commonly serum prostate-specific antigen (PSA) levels, T stage (size of tumor/spread to nearby tissues), percentage of cancer positive biopsy cores, and patient age are taken into account (D’Amico et al., 1998; Thompson et al., 2007; Cooperberg et al., 2009; Chang et al., 2014).