‘Thursday’s child has far to go’—interpreting subgroups and the STAMPEDE trial

STAMPEDE is a multi-arm multi-stage randomised controlled trial protocol, recruiting men with locally advanced or metastatic prostate cancer who are commencing long-term androgen deprivation therapy. Opening to recruitment with five research questions in 2005 and adding in a further five questions over the past 6 years, it has reported survival data on 6 of these 10 RCT questions over the past 2 years [1–3]. Some of these results have been of practice-changing magnitude [4, 5], but, in conversation, we have noticed some misinterpretation, both over-interpretation and under-interpretation, of subgroup analyses by the wider clinical community which could impact negatively on practice. We suspect, therefore, that such problems in interpretation may be common. Our intention here is to provide comment on interpretation of subgroup analysis in general using examples from STAMPEDE. Specifically, we would like to highlight some possible implications from the misinterpretation of subgroups and how these might be avoided, particularly where these contravene the very design of the research question. In this, we would hope to contribute to the conversation on subgroup analyses [6–11].

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