Use of Concomitant Androgen Deprivation Therapy in Patients Treated with Early Salvage Radiotherapy for Biochemical Recurrence After Radical Prostatectomy: Long-term Results from a Large, Multi-institutional Series

Abstract

Background: Hormonal manipulation concomitant to salvage radiotherapy (SRT) given for biochemical recurrence (BCR) after radical prostatectomy (RP) improved outcomes in two randomized trials. However, neither of these studies focused on men treated at low prostate-specific antigen (PSA) levels.

Objective: To test if the impact of androgen deprivation therapy (ADT) on metastasis in patients undergoing early SRT varies according to prostate cancer (PCa) features.

Design, setting, and participants: A total of 525 patients received SRT at PSA levels ≤2ng/ml.

Outcome measurements and statistical analyses: Multivariable Cox regression analyses assessed factors associated with metastasis. We tested the hypothesis that the impact of ADT varied according to the risk of metastasis. An interaction with groups (concomitant ADT vs no ADT) and the probability of distant metastasis according to a newly developed model was tested. A nonparametric curve explored the relationship between the risk of metastasis and 10-yr metastasis rates according to ADT.

Results and limitations: Median PSA and radiotherapy dose were 0.42ng/ml and 66Gy, respectively. Overall, 178 (34%) patients received ADT. At a median follow-up of 104 mo, 71 patients experienced metastasis. Grade group ≥4 (hazard ratio [HR]: 1.66; 95% confidence interval [CI]: 1.01-3.30), pT3b/4 (HR: 2.61; 95% CI: 1.51-4.52), and dose (HR: 0.82; 95% CI: 0.76-0.89) were associated with metastasis. The impact of ADT differed according to the risk of metastasis calculated using a multivariable model (p=0.01). This was confirmed when considering patients treated with early SRT (p=0.046), where ADT was associated with a reduction in the rate of metastasis only in eSRT; patients with more aggressive characteristics (ie, pT3b/4 and grade group ≥4, or pT3b/4 and PSA at eSRT ≥0.4ng/ml).

Conclusions: The beneficial effect of ADT concomitant to eSRT varied significantly according to disease characteristics, such that only men with more aggressive PCa features benefit from ADT in the eSRT setting for BCR after RP.

Patient summary: The oncological benefits of concomitant androgen deprivation therapy (ADT) in patients undergoing salvage radiotherapy (SRT) vary according to pathological characteristics. Only patients with more aggressive disease characteristics seemed to benefit from the use of hormonal manipulation at the time of early SRT. Conversely, the potential side effects of ADT could be spared in patients with low prostate-specific antigen levels and favorable pathological features.

Keywords: Androgen deprivation therapy; Prostate cancer; Radical prostatectomy; Salvage radiotherapy.