Survival outcomes in men with unfavorable intermediate-risk and high-risk prostate cancer treated with prostate-only versus whole pelvic radiation therapy.

Abstract

264 Background: Men with unfavorable intermediate-risk (UIR-PCa) or high-risk prostate cancer (HR-PCa) are often treated with definitive external beam radiotherapy (EBRT) plus androgen deprivation therapy (ADT). Treatment is frequently intensified by electively treating the pelvic lymph nodes with whole pelvis radiotherapy (WPRT), but practice patterns differ and the benefits of WPRT are not clearly defined, with mixed results from clinical trials. The recent POP-RT trial showed improved biochemical control with WPRT but most patients were staged with PET/CT scan. We hypothesized that men treated with WPRT would have improved overall survival (OS) relative to men treated with prostate-only radiotherapy in patients staged using conventional imaging. Methods: Men diagnosed between 2008-2015 with UIR or high-risk prostate cancer were retrospectively reviewed from the National Cancer Database (n = 28,724). Patients with involved nodes or distant metastases were excluded. Men received EBRT to a dose of 72-86.4 Gy and either prostate-only RT ± ADT (n = 13,549) or WPRT plus prostate RT ± ADT (n = 15,175). WPRT was delivered using a dose range of 40-50.4 Gy (1.8 – 2.0 Gy/fraction). The MSKCC nomogram was used to calculate risk of lymph node involvement. Unweighted or inverse probability of treatment weighting (IPTW) was used to perform multivariable analysis (MVA) using Cox regression modeling to compare OS hazard ratios, accounting for age, race, year of diagnosis, Charlson-Deyo comorbidity score, insurance status, education, income, treatment facility type, PSA, Gleason score, clinical T-stage, use of ADT, lymph node risk score, and radiation dose. Results: 53% of men received WPRT, with national utilization of WPRT increasing from 2008 to 2015. For every 1% increase in risk of lymph node involvement, there was a 1% increased risk of death ( P<.001). WPRT trended toward improved OS in all men with UIR or high-risk (Hazard Ratio (HR): 0.95 [95% Confidence Interval: 0.90-1.006], P=.07). WPRT correlated with improved OS in men with grade group 5 (GG5) disease (HR: 0.87 [0.78-0.98]. P=.02) or risk of lymph node involvement ≥ 10% (HR: 0.93 [0.87-0.99], P=.03). Conclusions: WPRT is associated with improved OS in men with a lymph node risk score ≥ 10% or GG5 disease. These results complement the recent POP-RT randomized trial in mostly PET/CT-staged patients, demonstrating that a more heterogenous population of men staged without functional imaging appears to benefit from WPRT.