Do diagnostic delays in cancer matter?

The United Kingdom has poorer cancer outcomes than many other countries due partly to delays in diagnosing symptomatic cancer, leading to more advanced stage at diagnosis. Delays can occur at the level of patients, primary care, systems and secondary care. There is considerable potential for interventions to minimise delays and lead to earlier-stage diagnosis. Scoping review of the published studies, with a focus on methodological issues. Trial data in this area are lacking and observational studies often show no association or negative ones. This review offers methodological explanations for these counter-intuitive findings. While diagnostic delays do matter, their importance is uncertain and must be determined through more sophisticated methods.