Optimizing Treatment in Intermediate-Risk Prostate Cancer: Secondary Analysis of a Randomized Phase 3 Trial

Abstract

Purpose: To identify patients with intermediate-risk prostate cancer (IRPC) benefiting from de-escalation of androgen deprivation therapy (ADT) and/or dose escalated radiation therapy (DERT), we performed a secondary analysis of a phase 3 trial by measuring biochemical failure (BF), distant metastases, prostate cancer-specific mortality, overall survival (OS), and distant metastases-free survival (DMFS) rates according to prognostic intermediate risk factors (IRF).

Methods and materials: The initial trial randomized 600 patients with IRPC to a 3-arm trial with 200 patients per arm, consisting of 6 months of ADT plus 70 Gy radiation therapy (ADT + RT70) versus ADT plus a DERT of 76 Gy (ADT + DERT76) versus DERT of 76 Gy alone (DERT76). We performed an analysis based on IRF: clinical stage, prostate-specific antigen level, Gleason score, percentage of positive biopsy cores (PBC) ≥50%, and Gleason pattern. Patients were allocated to 2 groups: favorable intermediate risk (FIR), defined as patients with only 1 IRF without Gleason pattern 4 + 3 or PBC ≥50%; and unfavorable intermediate risk (UIR), defined as all other patients. BF, distant metastases, prostate cancer-specific mortality, OS, and DMFS were compared between FIR and UIR.

Results: The median follow-up was 11.3 years (interquartile range, 10.9-11.7). In the FIR cohort, BF and OS were not significantly different between arms. UIR patients had significantly worse DMFS (hazard ratio [95% confidence interval], 1.61 [1.20-2.15]; P = .026) and OS (1.51 [1.12-2.04]; P = .0495) and a nonsignificant higher cumulative incidence of BF rate (1.55 [0.98-2.47]; P = .08). In UIR patients, a significant improvement in BF was seen in the arms receiving ADT compared to DERT76 alone. On multivariable analysis, Gleason pattern 4 + 3 and prostate-specific antigen >10 ng/mL independently affected BF and OS, regardless of the treatment arm.

Conclusions: In IRPC, therapeutic optimization appears possible. To avoid ADT side effects, DERT76 alone appears sufficient in patients harboring only 1 risk factor without Gleason pattern 4 + 3 and PBC ≥50% (FIR). All other UIR patients seem to benefit from ADT + DERT76.