Nationwide bowel cancer screening programme in England: cohort study of lifestyle factors affecting participation and outcomes in women

Background: In 2006, the National Health Service Bowel Cancer Screening Programme in England (NHSBCSP) began offering routine population-based biennial faecal occult blood testing (FOBt) at ages 60-69. There is, however, limited information on how characteristics of individuals affect participation and outcomes of screening, and we studied this association by linking NHSBCSP data to a large prospective cohort of women. Methods: Electronic linkage of the NHSBCSP and Million Women Study records identified 899 166 women in the study cohort with at least one invitation for screening. NHSBCSP provided information on screening acceptance, FOBt results, screen-detected colorectal cancer and other outcomes. The Million Women Study provided prospectively collected information on personal and lifestyle factors. Multiple regression was used to estimate relative risks (RRs) of factors associated with acceptance and outcomes of screening. Results: Overall, 70% of women (628 976/899 166) accepted their first invitation for bowel cancer screening, of whom 9133 (1.5%) were FOBt-positive, 743 (0.1%) had screen-detected colorectal cancer and 3056 (0.5%) had screen-detected colorectal adenoma. Acceptance was lower in women from the most than the least deprived tertile, in South Asians and in Blacks than in Whites, in current than in never smokers and in obese than in normal weight women: adjusted RRs (95% confidence interval) for acceptance vs not, 0.90 (0.90-0.90); 0.77 (0.75-79); 0.94 (0.92-0.96); 0.78 (0.77-0.78); and 0.88 (0.88-0.89), respectively: P<0.001 for each. These factors were also associated with an increased risk of being FOBt-positive and of having screen-detected adenoma, but were not strongly associated with the risk of screen-detected colorectal cancer. Relative risks for screen-detected adenoma were 1.22 (1.12-1.34), 2.46 (1.75-3.45), 1.61 (1.05-2.48), 1.53 (1.38-1.68) and 1.77 (1.60-1.95), respectively (P<0.001 for all, except for Blacks vs Whites P = 0.03). Use of hormone therapy for menopause was associated with reduced risk of screen-detected adenoma, RR ever vs never use, 0.87 (0.81-0.93), P<0.001 and colorectal cancer, 0.78 (0.68-0.91), P = 0.001. Interpretation: Among women in England, socioeconomic and lifestyle factors strongly affect participation in routine bowel cancer screening, risk of being FOBt-positive and risk of having screen-detected colorectal adenoma. However, screen-detected colorectal cancer risk is not strongly related to these factors.