Long-term outcomes of prostate radiotherapy for newly-diagnosed metastatic prostate cancer

In patients presenting with metastatic prostate cancer, the role of local therapy is evolving. Two recently reported large-scale randomized trials suggest that radiotherapy (RT) directed at the prostate improves overall survival (OS) in patients with low metastatic burden. We reviewed the experience of prostate RT in this setting at our center. The study population consisted of men with newly-diagnosed metastatic hormone-sensitive prostate cancer (mHSPC) referred to a comprehensive cancer center between 2005 and 2015 and treated initially with androgen deprivation therapy. Patients were eligible for inclusion if they received (1) prostate RT with biological effective dose (BED) at least that of a course of 40 Gy in 15 fractions or (2) no prostate RT. The association between receipt of prostate RT and OS was studied. OS was estimated using the Kaplan–Meier method and Cox regression was used to identify factors associated with OS. The cohort consisted of 410 patients, of whom 128 received prostate RT. Median follow-up 61.0 months. On univariate analysis, receipt of prostate RT was associated with improved OS (HR 0.59, 95% CI 0.45–0.77, p = 0.0001). Median OS in those patients receiving prostate RT was 47.4 months versus 26.3 months in those not receiving prostate RT. In a multivariate Cox model, receipt of prostate RT remained associated with improved OS (HR 0.69, 95% CI 0.50–0.94, p = 0.02). In those treated with prostate RT, increasing BED was also associated with improved OS (HR 0.87 per 10 Gy increase, 95% CI 0.76–0.99, p = 0.03). This cohort represents the largest single-center experience of primary tumor-directed RT in mHSPC reported to date. In this population, receipt of prostate RT was associated with improved OS and the magnitude of the OS benefit was clinically significant. The possibility of an RT dose-response gradient in this setting merits further study.