Postrandomization analysis assessing survival following radiation therapy (RT) with or without 6 months of androgen suppression therapy (AST) for localized prostate cancer (PCa)

Abstract

5129 Background: 6 months of AST+RT was shown to improve survival vs. RT alone in men with unfavorable-risk localized PCa, but it is unknown if this benefit applied to all risk subgroups. Methods: Among 206 men with clinical T1b-T2b PCa and at least 1 unfavorable feature (PSA>10 or Gleason >=7 or MRI evidence of T3 disease) randomized to 70Gy of RT with or without 6 months of AST, we performed post-randomization subgroup analyses within four subgroups defined by both risk group (high risk [Gleason 8–10 or PSA >20] or intermediate risk [all others]), and by ACE-27 comorbidity level (no/limited comorbidity or moderate/severe comorbidity). Within the 4 subgroups a log-rank test was used to compare Kaplan Meier estimates of survival (requiring p < 0.05/4 or p < 0.0125 to adjust for multiple comparisons) and within the 2 risk groups we used Cox multivariable analysis (MVA) to assess the association of treatment with the risk of death after adjusting for known prognostic factors. Results: After a median follow-up 8.2 yrs, 74 men died. In men with no or minimal comorbidity, estimates of survival were significantly higher among those who received AST+RT vs. RT alone, regardless of whether they had intermediate risk disease (90.9 vs. 85.8% at 7yrs, p = 0.009) or high-risk disease (88.9% vs. 51.2% at 7yrs, p = 0.007). In men with moderate or severe comorbidity, no difference in survival was observed after AST+RT vs. RT in intermediate risk (p = 0.2) or high risk (p = 0.5). After adjusting for known prognostic factors, treatment with RT as compared to AST+RT was associated with an increased risk of death in men with intermediate (AHR: 3.0 [95% CI: 1.3 to 7.2]; p = 0.01) and high risk disease (AHR: 3.3 [95% CI: 0.94 to 11.3]; p = 0.06) in a model that adjusted for the interaction between treatment and comorbidity. Conclusions: Among men with T1b-T2b prostate cancer who have no or minimal comorbidity, the addition of 6 months of AST to RT was associated with improved survival in men with both intermediate risk and high-risk disease. Among men with moderate to severe comorbidity, neither risk group appeared to benefit from the addition of AST. No significant financial relationships to disclose.