The impact of prostate-specific antigen persistence after radical prostatectomy on the efficacy of salvage radiotherapy in patients with primary N0 prostate cancer

Objective To test whether salvage radiotherapy (SRT) in patients with lymph node negative (N0) prostate cancer is equally effective with persistent prostate-specific antigen (PSA) and PSA rising from the undetectable range (<0.1 ng/mL) after radical prostatectomy (RP). Patients and methods We assessed post-SRT PSA progression-free survival (PFS) in 555 patients with prostate cancer. The entire cohort was compared with a risk-adjusted subgroup of 112 patient pairs with matching pre-RP PSA level (+/- 10 ng/mL), Gleason score (<= 6 vs 7 vs >= 8), and pre-SRT PSA level (+/- 0.5 ng/mL). Results The median follow-up was 6.1 years. After RP, PSA was undetectable in 422 and persistent in 133 patients. PSA persistence and a pre-SRT PSA level of >= 0.5 ng/mL reduced Kaplan-Meier rates of PFS significantly. In multivariate analysis of the entire cohort and after risk adjustment, the pre-SRT PSA level but not post-RP PSA persistence was a significant parameter. In the matched cohort's subgroup with early SRT at a PSA level of <0.5 ng/mL, a trend towards a worse outcome with post-RP PSA persistence was observed. Delayed SRT with a PSA level >= 0.5 ng/mL led to a PFS of <30%, irrespective of the post-RP PSA level. Conclusion In patients with N0 prostate cancer with post-RP PSA persistence, early SRT at a PSA level RP undetectable PSA. They might benefit from intensified therapy, but larger case numbers are required to substantiate this conclusion. In patients with a PSA level >= 0.5 ng/mL and higher-risk features associated with post-RP PSA persistence, SRT alone is unlikely to provide long-term freedom from further progression.