Background: Current recommendations regarding radiotherapy treatment for unfavorable intermediate-risk prostate cancer (UIR-PCa) include external beam radiotherapy (EBRT) ± brachytherapy boost (BT) ± androgen deprivation therapy (ADT). The ideal radiotherapy treatment approach for UIR-PCa has not been well-defined. We hypothesized that EBRT+BT±ADT is associated with improved overall survival (OS) relative to EBRT±ADT in men with UIR-PCa.
Materials and methods: The National Cancer Database (NCDB) was used to retrospectively identify 32,246 men diagnosed between 2004 and 2015 with UIR-PCa who received EBRT (n = 13,265), EBRT+ADT (n = 13,123), EBRT+BT (n = 3440), or EBRT+BT+ADT (n = 2418). OS was the primary outcome. Inverse probability of treatment weighting was used to adjust for covariable imbalances and weight-adjusted multivariable analysis using Cox regression modeling was used to compare OS hazard ratios.
Results: Median follow-up was 60 months (range: 3-168 months). EBRT+ADT correlated with improved OS relative to EBRT alone on multivariable analysis (Hazard Ratio (HR): 0.92, [95% Confidence Interval: 0.87-0.98], p = 0.005). Compared to EBRT+ADT, EBRT+BT (HR: 0.77 [0.69-0.85], p = 3 × 10-7) and EBRT+BT+ADT (HR: 0.75 [0.67-0.83], p = 6 × 10-8) were associated with improved OS. Eight-years OS for the EBRT+ADT versus EBRT+BT+ADT was 70% and 78% (p < 0.0001), which is similar to historical clinical trials (ASCENDE-RT 9-year OS: 74% vs. 78%, p = 0.29). Relative to EBRT+BT, EBRT+BT+ADT was not associated with improved OS (HR: 0.99 [0.87-1.11], p = 0.82).
Conclusions: In a large retrospective cohort, the addition of brachytherapy to EBRT correlated with improved survival in men with UIR-PCa. Men receiving EBRT+ADT+BT had improved OS relative to EBRT+ADT. The addition of ADT to EBRT, but not to EBRT+BT, correlated with improved OS.
Keywords: Brachytherapy; Intermediate-risk; Prostate cancer; Radiation treatment; Radiotherapy; Unfavorable intermediate-risk.
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