# Invitation for FOBt screening and colorectal cancer mortality: A prospective analysis in the Million Women Study cohort

## TL;DR

This study analyzed the effectiveness of a colorectal cancer screening program in women and found no overall reduction in cancer deaths, but some benefits for distal colon cancer.

## Contribution

The study used a quasi-randomized design to estimate real-world screening effectiveness and found site-specific differences in outcomes.

## Key findings

- No significant overall reduction in colorectal cancer mortality from screening invitations.
- A reduction in deaths from distal colon cancer was observed.
- Differences in screening effectiveness were noted by anatomical sub-site.

## Abstract

Using linked data from the Million Women Study (MWS) cohort and the NHS Bowel Cancer Screening Programme (NHS BCSP) offering biennial guaiac faecal occult blood test (gFOBt) screening from 2006, we examined factors associated with screening acceptance, and differences in colorectal cancer (CRC) mortality by screening invitation status. Characteristics of attenders and non‐attenders were compared among 752,007 MWS participants born 1940–1950, who were all invited for at least one round of routine screening. Women declining screening had higher deprivation and smoking levels, and a 2‐fold risk of all‐cause and CRC mortality compared with women who accepted. Of 246,160 women born in 1935–1939, 111,956 were assigned to the “no intention to invite” group, and 134,204 to the “intention to invite” group based on year of birth and postcode sector, with an average of 0.01 and 2.40 screening invitations in each group, respectively. During a mean follow up of 11.9 years, there were 858 and 791 CRC deaths in the “intention to invite” and “no intention to invite” groups, respectively. In the period 4 or more years after study entry there was no significant reduction in risk of death from CRC associated with invitation for screening (RR = 0.94, 95%CI 0.83–1.06), but evidence of differences in associations by anatomical sub‐site, with a reduction in deaths from distal colon cancer (0.64, 0.47–0.88), but not proximal (1.02, 0.83–1.25) or rectal cancer (0.97, 0.79–1.20) (p‐value for heterogeneity by subsite = 0.05). Investigation of the effectiveness of current bowel screening methods using faecal immunochemical testing (FIT) by sex and cancer sub‐site is warranted.

What's new?

The screening effectiveness of population screening programmes can differ from the screening efficacy measured in randomised controlled trials and is often difficult to measure directly. The authors used data on a subset of women born between 1935 and 1939 from the Million Women Study to estimate the effect of screening on colorectal cancer mortality using a quasi‐randomised trial design. There was no clear reduction in the risk of death from colorectal cancer associated with invitation for screening. Differences in associations were observed by anatomical sub‐site, with a reduction in deaths from distal but not proximal colon or rectal cancer.