Identifying Appropriate Patients for Early Salvage Radiotherapy after Prostatectomy

Abstract

It remains unclear whether relapsed prostate specific antigen at postprostatectomy salvage radiotherapy impacts outcomes as long it is 1.0 ng/ml or less. We performed a retrospective cohort study of 197 patients treated with salvage radiotherapy in the setting of detectable relapsed prostate specific antigen 1.0 ng/ml or less. Patients were excluded from analysis if they had lymph node involvement or received androgen deprivation therapy. Freedom from prostate specific antigen progression after salvage radiotherapy was analyzed by a Cox regression model. Median relapsed prostate specific antigen was 0.33 ng/ml (range 0.07 to 1.0). There was 86% freedom from prostate specific antigen progression at a median followup of 52 months. Relapsed prostate specific antigen (HR 1.9, p = 0.004), Gleason score 8-10 (HR 5.2, p <0.001) and negative margin status (HR 2.0, p = 0.02) were independently associated with an increased risk of prostate specific antigen progression after salvage radiotherapy. We identified interaction between relapsed prostate specific antigen and Gleason score (p = 0.04) but not margin status. A significant association was noted between higher relapsed prostate specific antigen and prostate specific antigen progression after salvage radiotherapy in patients with Gleason score 8-10 but not 7 or less. In patients with Gleason score 8-10 the rate of freedom from prostate specific antigen progression at 53 months was 77% vs 26% when salvage radiotherapy was initiated at a relapsed prostate specific antigen of 0.33 or less vs 0.34 to 1.0 ng/ml (log rank p = 0.003). Different relapsed prostate specific antigen thresholds for unsuccessful salvage radiotherapy may exist based on Gleason score. These data suggest that patients with Gleason score 8-10 should be offered salvage radiotherapy at the earliest detectable relapsed prostate specific antigen, even 0.33 ng/ml or less. Those with Gleason score 7 or less may have the opportunity to be followed with serial prostate specific antigen measurements to improve risk stratification, and delay and/or avoid the potential toxicity of salvage radiotherapy.