Abstract 3438: Whole pelvis versus prostate-only radiotherapy with or without short course androgen deprivation therapy and mortality risk

Purpose: To determine whether extent of prostate radiotherapy (i.e. whole-pelvic radiotherapy (WPRT) versus prostate/seminal-vesicle radiotherapy [PSVRT]) is associated with all-cause mortality (ACM) in men treated with or without androgen deprivation therapy (ADT). Methods: A multi-institutional cohort of 3,709 prostate cancer patients was prospectively assembled from 1991-2006. Median age was 72 years and all patients had T1c-T3N0M0 adenocarcinoma of the prostate. Patients were treated with WPRT or PSVRT followed by a brachytherapy boost, with or without neoadjuvant ADT (median duration 4.2months). 70% of patients had unfavorable-risk disease (Gleason ≥7; PSA ≥10ng/mL; or stage ≥T2b). Cox regression was applied to determine whether the radiation treatment volume affected the risk of ACM. A test for interaction between radiation volume and ADT use was conducted. Results: After a median follow-up of 3.3 years, 561 deaths were observed. A decreased risk of ACM was noted with the use of WPRT versus PSVRT (adjusted hazard ratio [AHR] 0.58; 95% confidence interval [CI] 0.38-0.89; p = 0.01), or with ADT (AHR 0.71; 95%CI 0.58-0.90; p = 0.004). However, combining WPRT and ADT did not further improve ACM in comparison to either WPRT alone or PSVRT with ADT. Moreover, there was a significant interaction between the RT treatment volume and ADT (AHR 1.61; 95%CI 1.004-2.58; p = 0.048). Conclusions: Treatment with WPRT or short-course ADT is associated with a decreased risk of ACM, though combining the two does not yield greater benefit. This observation suggests a shared mechanism for this risk-reduction which we hypothesize to be sterilization of micrometastatic disease within the pelvic lymph nodes. Citation Format: Lior Z. Braunstein, Ming-Hui Chen, Daniel E. Dosoretz, Sharon Salenius, Michael Katin, Akash Nanda, Anthony V. D'Amico. Whole pelvis versus prostate-only radiotherapy with or without short course androgen deprivation therapy and mortality risk. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3438. doi:10.1158/1538-7445.AM2015-3438