Recently, the results of the STAMPEDE trial arm H were reported. This trial investigated the effect of radiotherapy to the prostate only on the overall survival of patients with metastatic prostate cancer. Although on the whole the findings of the trial were negative, a significant increase in survival was noted in the prespecified subgroup of patients with a low metastatic burden. As only a few analyses were prespecified, the direction of the subgroup effect was prespecified and consistent with previous observations from the separate but comparable HORRAD trial. The subgroup effect was large and independent of other subgroup variables, and as there is a solid biological rationale for these results, they are to be considered trustworthy, and are likely to change clinical practice. Further research should focus on better specification of the low metastatic burden subgroup, if other locally ablative treatments such as surgery are equivalent, and if ablation of all metastatic lesions would give additional benefit
