Observation with or without late radiotherapy is equivalent to early radiotherapy in high-risk prostate cancer after radical prostatectomy: A SEER-Medicare analysis on trends, survival outcomes and complications

Introduction: While early radiotherapy (eRT) after radical prostatectomy (RP) has shown to improve oncologic outcomes in patients with high-risk prostate cancer (PCa) in a recent clinical trial, controversy remains regarding its benefit. We aimed to illustrate national trends of post-RP radiotherapy and compare outcomes and toxicities in patients receiving eRT vs. observation with or without late radiotherapy (lRT). Methods: Utilizing the Surveillance, Epidemiology and End Results (SEER)-Medicare data from 2001 to 2011, we identified 7557 patients with high-risk pathologic features after RP (≥ pT3N0 and/or positive surgical margins). Our study cohort was consisted of patients receiving RT within 6 months of surgery (eRT), those receiving RT after 6 months (IRT), and those never receiving RT (observation). Another subcohort, delayed RT (dRT), encompassed both IRT and observation. Trends of post-RP radiotherapy were compared using the Cochran-Armitage trend test. Cox regression models identified factors predictive of worse survival outcomes. Kaplan-Meier analyses compared the eRT and the dRT groups. Results: Among those with pathologically confirmed high-risk PCa after RP, 12.7% (n=959), 13.2% (n=1710), and 74.1% (n=4888) underwent eRT, lRT, and observation without RT, respectively. Of these strategies, the proportion of men on observation without RT increased significantly over time (p=0.004). Multivariable Cox regression model demonstrated similar outcomes between the eRT and the dRT groups. At a median follow up of 5.9 years, five-year overall and cancer-specific survival outcomes were more favorable in the dRT group, when compared to the eRT group. Radiation related toxicities, including urinary incontinence, erectile dysfunction, and urethral stricture, were higher in the eRT group when compared to the lRT group. Conclusions: Our results suggest that a blanket adoption of the eRT in high-risk PCa based on clinical trials with limited follow up may result in overtreatment of a significant number of men and expose them to unnecessary radiation toxicity.