PURPOSEWe assessed the association of quantitative clinical and pathologic information, including serum and tissue pro-prostate-specific antigen (proPSA) measurements, with outcomes among men with prostate cancer in an expectant management (active surveillance) program.EXPERIMENTAL DESIGNWe identified 71 men enrolled in expectant management with frozen serum and tissue available from diagnosis: 39 subsequently developed unfavorable biopsies (Gleason score > or =7, > or =3 cores positive for cancer, >50% of any core involved with cancer), whereas 32 maintained favorable biopsies (median follow-up, 3.93 years). Serum total PSA, free PSA (fPSA), and [-2]proPSA were measured by the Beckman Coulter immunoassay. [-5/-7]proPSA was evaluated in cancer and benign-adjacent areas (BAA) by quantitative immunohistochemistry. Cox proportional hazards and Kaplan-Meier analyses were used to identify significant associations with unfavorable biopsy conversion.RESULTSThe ratio [-2]proPSA/% fPSA in serum was significantly higher at diagnosis (0.87 +/- 0.44 versus 0.65 +/- 0.36 pg/mL; P = 0.02) in men developing unfavorable biopsies. [-5/-7]proPSA tissue staining was more intense (4104.09 +/- 3033.50 versus 2418.06 +/- 1606.04; P = 0.03) and comprised a greater fractional area (11.58 +/- 7.08% versus 6.88 +/- 5.20%; P = 0.01) in BAA of these men. Serum [-2]proPSA/% fPSA [hazard ratio, 2.53 (1.18-5.41); P = 0.02], BAA [-5/-7]proPSA % area [hazard ratio, 1.06 (1.01-1.12); P = 0.02] and BAA [-5/-7]proPSA stain intensity [hazard ratio, 1.000213 (1.000071-1.000354); P = 0.003] were significantly associated with unfavorable biopsy in Kaplan-Meier and Cox analyses. Serum [-2]proPSA/% fPSA significantly correlated with BAA [-5/-7]proPSA % area (rho = 0.40; P = 0.002) and BAA [-5/-7]proPSA stain intensity (rho = 0.33; P = 0.016).CONCLUSIONSIn a prospective cohort of men enrolled into expectant management for prostate cancer, serum and tissue levels of proPSA at diagnosis are associated with need for subsequent treatment. The increase in serum proPSA/% fPSA might be driven by increased proPSA production from "premalignant" cells in the prostate BAA.