Effect of Prior Local Therapy on Response to First-line Androgen Receptor Axis Targeted Therapy in Metastatic Castrate-resistant Prostate Cancer: A Secondary Analysis of the COU-AA-302 Trial

Abstract

Background: Men with localized prostate cancer are often treated with local therapy (LT). However, a proportion of these patients will eventually develop recurrence and progression requiring systemic therapy. Whether primary LT affects the response to this subsequent systemic treatment is unclear.

Objective: We investigated whether the receipt of prior prostate-directed LT influenced the response to first-line systemic therapy and survival in docetaxel-naïve metastatic castrate-resistant prostate cancer (mCRPC) patients.

Design, setting, and participants: This is an exploratory analysis of the COU-AA-302 trial, a multicentric double-blinded phase 3 randomized controlled trial in which mCRPC patients with no to mild symptoms were randomized to receive abiraterone plus prednisone or placebo plus prednisone.

Outcome measurements and statistical analysis: We compared the time-varying effects of first-line abiraterone in patients with and without prior LT using a Cox proportional hazard model. The cut points were chosen using grid search, and were 6 and 36 mo for radiographic progression-free survival (rPFS) and overall survival (OS), respectively. We also investigated whether there was any difference in treatment effect on score change (relative to baseline) in various patient-reported outcomes (measured by Functional Assessment of Cancer Therapy-Prostate [FACT-P]) over time depending on the receipt of prior LT. The adjusted association of prior LT with survival was determined using weighted Cox regression models.

Results and limitations: Among 1053 eligible patients, 64% (n = 669) received prior LT. We did not find any statistically significant heterogeneity of time-dependent treatment effect from abiraterone on rPFS in patients with (hazard ratio [HR]: 0.36 [95% confidence interval: 0.27-0.49] at ≤6 mo; 0.64 [0.49-0.83] at >6 mo) or without (HR: 0.37 [0.26-0.55] at ≤6 mo; 0.72 [0.50-1.03] at >6 mo) prior LT. Similarly, there was no significant heterogeneity in time-dependent treatment effect on OS with (HR: 0.88 [0.71-1.10] at ≤36 mo; 0.76 [0.52-1.11] at >36 mo) or without (0.78 [0.60-1.01] at ≤36 mo; 0.55 [0.30-0.99] at >36 mo) prior LT. We did not find sufficient evidence of a difference in treatment effect from abiraterone on score change over time in prostate cancer subscale (interaction p = 0.4), trial outcome index (interaction p = 0.8), and FACT-P total score (interaction p = 0.6) depending on the receipt of prior LT. Receipt of prior LT was associated with a significant improvement in OS (average HR: 0.72 [0.59-0.89]).

Conclusions: This study demonstrates that the efficacy of first-line abiraterone and prednisone in docetaxel-naïve mCRPC do not vary significantly based on the receipt of prior prostate-directed LT. Further studies are needed to explore the plausible mechanisms of the association of prior LT with superior OS.

Patient summary: This secondary analysis of the COU-AA-302 trial suggests that survival benefits and temporal changes in quality of life with first-line abiraterone in docetaxel-naïve mCRPC do not differ significantly among patients who received versus those who did not receive prior prostate-directed local therapy.

Keywords: Abiraterone; Local therapy; Metastatic castrate-resistant prostate cancer; Radiation therapy; Radical prostatectomy.