Men with newly diagnosed, metastatic prostate cancer are typically treated with systemic therapy, including androgen deprivation therapy (ADT), and receive local therapy for symptom palliation if needed. However, retrospective data suggest that local radiotherapy to the primary tumor may have an impact on survival in metastatic prostate cancer and patients with better prognoses may benefit the most from this approach. This hypothesis was tested within the multiarm, multistage STAMPEDE protocol, which is evaluating several treatment approaches for newly diagnosed, metastatic prostate cancer in an attempt to improve long-term outcomes. At the 2018 European Society for Medical Oncology (ESMO) Congress Presidential Symposium, Chris Parker, MD (The Royal Marsden NHS Foundation Trust, Sutton, United Kingdom), presented results from a randomized, phase III trial of 2061 patients with metastatic, newly diagnosed prostate cancer who were randomized to receive either ADT with or without docetaxel (SOC) or SOC plus prostate radiotherapy (RT). These results were also simultaneously published in The Lancet.
The study failed to meet its primary endpoint of improved overall survival (OS) with the addition of RT to SOC in unselected patients with newly diagnosed, metastatic prostate cancer. The 3-year OS was 65% with RT plus SOC, compared to 62% for SOC alone (HR 0.92, P = .266). However, in patients with a low metastatic disease burden, there was a clear OS benefit from RT plus SOC. In this population, the 3-year OS was 81% for patients receiving RT plus SOC, compared to 73% for patients receiving SOC alone (HR 0.68; P = .007). Furthermore, RT plus SOC significantly improved rates of failure-free survival (FFS) at 3 years compared to SOC in the entire trial population (32% vs 23%; HR 0.76; P<.0001). Prostate radiotherapy was well tolerated.
Dr Parker concluded that, while RT plus SOC did not improve survival in the entire patient population, the benefit in patients with low metastatic burden was significant and supports this approach as a standard treatment option for these patients. In his discussion of this abstract, Robert Bristow, MD, PhD (Manchester Cancer Research Center, Manchester, United Kingdom), agreed, indicating that these are practice-changing results and RT should be added to SOC systemic therapy in men with newly diagnosed prostate cancer with low metastatic disease burden. Moreover, based on retrospective data and extrapolation, a similar treatment approach should be considered for M0 patients with N1 disease. Dr Bristow highlighted that markers in responders and nonresponders from this trial need to be evaluated and that future trials will answer several questions related to the role of different RT volumes, prostate surgery versus radiotherapy, modern imaging, and contemporary systemic therapies (including immunotherapy).