A prospective cohort and extended comprehensive-cohort design provided insights about the generalizability of a pragmatic trial: the ProtecT prostate cancer trial

Randomized controlled trials (RCTs) deliver robust internally valid evidence but generalizability is often neglected. Design features built into the ProtecT RCT of treatments for localized prostate cancer (PCa) provided insights into its generalizability.

Population-based cluster-randomization created a prospective study of PSA-testing and a comprehensive-cohort study including groups choosing treatment or excluded from the RCT, as well as those randomized. Baseline information assessed selection and response during RCT conduct.

The prospective study (82,430 men PSA-tested) represented healthy men likely to respond to a screening invitation. The extended comprehensive-cohort comprised 1,643 randomized, 997 choosing treatment, and 557 excluded with advanced cancer/comorbidities. Men choosing treatment were very similar to randomized men except for having more professional/managerial occupations. Excluded men were similar to the randomized socio-demographically but different clinically, representing less healthy men with more advanced PCa.

The ProtecT RCT's design features provided data to assess the representativeness of the prospective cohort and generalizability of the RCT's findings. Greater attention to collecting data at the design stage of pragmatic trials would better support later judgements by clinicians/policy-makers about the generalizability of RCT findings in clinical practice.

Journal of clinical epidemiology. 2017 Dec 26 [Epub ahead of print]

Jenny L Donovan, Grace J Young, Eleanor I Walsh, Chris Metcalfe, J Athene Lane, Richard M Martin, Marta K Tazewell, Michael Davis, Tim J Peters, Emma L Turner, Nicola Mills, Hanan Khazragui, Tarnjit K Khera, David E Neal, Freddie C Hamdy, ProtecT study group

School of Social and Community Medicine, University of Bristol, Bristol, UK; NIHR Collaboration for Leadership in Applied Health Research and Care West, hosted by University Hospitals Bristol NHS Foundation Trust, Bristol, UK. Electronic address: ., School of Social and Community Medicine, University of Bristol, Bristol, UK., School of Social and Community Medicine, University of Bristol, Bristol, UK; Bristol Randomised Trials Collaboration, University of Bristol, UK, G Young, JA Lane, C Metcalfe., School of Social and Community Medicine, University of Bristol, Bristol, UK; University Hospitals Bristol NHS Foundation Trust National Institute for Health Research Bristol Nutrition Biomedical Research Unit., School of Clinical Sciences, University of Bristol, Bristol, UK., Nuffield Department of Surgical Sciences, John Radcliffe Hospital, University of Oxford, Oxford, UK.

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