Radiotherapy to the primary tumour for newly diagnosed, metastatic prostate cancer (STAMPEDE): a randomised controlled phase 3 trial

BACKGROUND: Local treatment of the prostate might not only improve local control, but also slow the progression of metastatic disease. We hypothesised that radiotherapy (RT) to the prostate would improve overall survival in men presenting with metastatic prostate cancer (PCa) and that the survival benefit would be greater in men with a lower metastatic burden. METHOD: STAMPEDE is a multi-arm multi-stage platform protocol that included a randomised phase III comparison to test the above hypotheses. Standard-of-care (SOC) was lifelong ADT, with up-front docetaxel permitted from Dec-2015. Stratified randomisation within 12 weeks on ADT allocated pts 1:1 to SOC or SOC+RT. Men allocated to RT received daily (55Gy/20f over 4 weeks) or weekly (36Gy/6f over 6 weeks) RT, started ≤8 weeks after randomisation or completion of docetaxel. The RT schedule was nominated before randomisation. The primary outcome measure was death from any cause; secondary outcome measures included failure-free survival (FFS). Comparison of SOC vs SOC+RT for survival had 90% power at 2.5% 1-sided alpha for hazard ratio (HR) of 0.75, requiring approximately 267 control arm deaths. Analyses used Cox proportional hazards & flexible parametric models, adjusted for stratification factors. A pre-specified subgroup analysis tested the effects of prostate RT by baseline metastatic burden. RESULTS: 2061 men with newly-diagnosed M1 PCa were randomised from Jan 2013 to Sep 2016. Randomised groups were well balanced: median age 68yrs; median PSA 97ng/ml; 18% early docetaxel; metastatic burden: 40% lower metastatic burden, 54% higher metastatic burden, 6% unknown in the group as a whole. Prostate RT improved FFS (HR=0.76, 95%CI 0.68, 0.84; p=3.36x10-7 60 ) but not overall survival (HR=0.92, 95%CI 0.80, 1.06; p=0.266). Pre-specified subgroup analysis showed 62 improved overall survival for prostate RT in 819 men with a lower metastatic burden 63 (HR=0.68, 95%CI 0.52, 0.90; p=0.007) but not in 1120 men with a higher metastatic burden (HR=1.07, 95%CI 0.90, 1.28; p=0.300). RT was well-tolerated during (G3-4 5% SOC+RT) and after treatment (G3-4 <1% SOC, 4% SOC+RT). CONCLUSIONS: Radiotherapy to the prostate did not improve survival for unselected patients with newly-diagnosed metastatic prostate cancer, but, in a pre-specified subgroup analysis, did improve survival in men with a lower metastatic burden. Therefore, prostate radiotherapy should be a standard treatment option for men with oligometastatic disease