Long-term effectiveness and overdiagnosis in the NHS breast screening programme: a cohort study with up to 33 years...

Population-based mammographic screening programmes have been operating for over 30 years and whilst many studies have assessed the short- to medium-term effectiveness of screening, few have assessed their long-term effectiveness. The aim of this study was to assess the long-term effectiveness of the NHS Breast Screening Programme in England and Wales.

2,509,384 women aged 49-64 years and uninvited to screening upon study entry were studied, with screening status changing on invitation and attendance. Women were followed for breast cancer diagnosis and death for a maximum of 33 years. Poisson regression was used to assess the effect of screening on breast cancer incidence and mortality compared to an uninvited comparison group, and overdiagnosis.

After adjustment for confounders, invitation to screening was associated with a 28% reduction in breast cancer mortality (RR: 0.72; 95% CI: 0.71-0.74) and attendance at screening was associated with a 33% reduction (RR: 0.67; 95% CI: 0.65-0.69). There was a 4% excess of breast cancer diagnoses associated with being screened (RR: 1.04; 95% CI: 1.02-1.07) with at least 5 years follow-up post-screening.

These findings indicate that screening continues to be effective in reducing breast cancer mortality many years after cessation of screening and that the level of overdiagnosis associated with long-term follow-up is low.