Significance of early prostate-specific antigen values after salvage radiotherapy in recurrent prostate cancer patients treated with surgery.

OBJECTIVES To assess the use of post-salvage radiotherapy prostate-specific antigen for early prediction of biochemical failure or clinical recurrence after salvage radiotherapy in recurrent prostate cancer patients after prostatectomy. METHODS From 2000 to 2011, 164 patients were treated with salvage radiotherapy alone for recurrent prostate cancer. Patients who received androgen deprivation therapy before or within 1 month of the termination of salvage radiotherapy were excluded. Survival analysis was carried out with: (i) a selected prostate-specific antigen reference value (0.2 ng/mL) at the second follow-up period (4 months) after salvage radiotherapy (prostate-specific antigen value over 0.2 ng/mL at post-salvage radiotherapy 4 months); and (ii) prostate-specific antigen percent decline (post-salvage radiotherapy 4 months prostate-specific antigen/pre-salvage radiotherapy prostate-specific antigen). RESULTS The median follow-up time was 53.4 months (range 8.5-134.1 months). The 5-year clinical recurrence-free survival was 87.9%. Prostate-specific antigen percent decline of 0.45 was set as the cut-off value for clinical recurrence-free survival based on the receiver operating characteristics curve. In the multivariate analysis, a prostate-specific antigen value over 0.2 ng/mL at post-salvage radiotherapy 4 months (P = 0.013) and prostate-specific antigen percent decline ≥ 0.45 (P = 0.002) were both significant parameters predicting clinical recurrence-free survival. Otherwise, prostate-specific antigen percent decline ≥ 0.45 was the only statistically significant predictor of biochemical failure-free survival (biochemical failure-free survival after salvage radiotherapy). CONCLUSIONS A prostate-specific antigen value over 0.2 ng/mL at post-salvage radiotherapy 4 months and prostate-specific antigen percent decline ≥ 0.45 are negative predictors of clinical recurrence-free survival after salvage radiotherapy. Prostate-specific antigen percent decline ≥ 0.45 is also associated with worse biochemical failure-free survival after salvage radiotherapy. Patients with delayed prostate-specific antigen decrease should be carefully observed for clinical recurrence.