Study snapshot

Who were involved? Approximately 370,000 individuals who were routinely invited for screening in the NHS Bowel Cancer Screening Programme (BCSP). Participants were randomly allocated either to receive an invitation letter with a GP endorsement or the standard letter sent out at the time by the BCSP without a GP endorsement.

Location: England

Dates: February to March 2016.

Overview

The ASCEND2 study was a collaboration between the NHS Bowel Cancer Screening Programme, University College London, Queen Mary University of London and the Cancer Screening & Prevention Research Group (CSPRG) at Imperial College London.

The trial is registered with the ISRCTN registry. Its unique number is 11660314.

The study was funded by Cancer Research UK.

Background

Colorectal cancer screening reduces cancer-specific mortality. Uptake in the national bowel cancer screening programme (BCSP) in England varies by socioeconomic status, which may lead to inequalities in cancer outcomes.

ASCEND2 evaluated the effect of general practitioner endorsement accompanying the screening kit rather than with the invitation letter on:

  • Participation in the BCSP.
  • The socioeconomic gradient in participation in the BCSP.

Method

The NHS BCSP in England is delivered via five regional hubs. In early 2016, we carried out a cluster-randomised trial, with hub-day of invitation as the randomisation unit. We randomised 150 hub-days of invitation to the intervention group, GP endorsement on the letter accompanying the guaiac faecal occult blood testing kit (75 hub-days, 197,366 individuals) or control, usual letter (75 hub-days, 197,476 individuals). The endpoint was participation, defined as return of a valid kit within 18 weeks of initial invitation. Because of the cluster randomisation, data were analysed by a hierarchical logistic regression, allowing a random effect for date of invitation. Socioeconomic status was represented by the index of multiple deprivation.

Results

Participation was 59.4% in the intervention group and 58.7% in the control group, a significant difference (p = 0.04). There was no heterogeneity of the effect of intervention by index of multiple deprivation. We found that there was some confounding between date and screening episode order (first or subsequent screen). This in turn may have induced confounding with age and slightly diluted the result.

General practitioner endorsement induced a modest increase in participation in bowel cancer screening, but did not affect the socioeconomic gradient. When considering cluster randomisation as a research method, careful scrutiny of potential confounding should be indicated in advance if possible and in analysis otherwise.

ASCEND2 results were published in the Journal of Medical Screening in 2021.