The influence of breast screening on breast cancer incidence in England: observational study based on cancer registries and bulletins of the NHS Breast Screening Programme.

BACKGROUND

To assess the amount of breast cancer overdiagnosis associated with the National Health Service Breast Screening Programme (NHSBSP) that started in 1988 in England.

METHODS

First, numbers of breast cancers in women eligible for breast screening not attending screening were estimated for the period 1995-2019, which were extrapolated to all women. A second method was based on ratios of incidence rates of breast cancers in women aged 50-69 to women aged 70 years or more in 1971-1985. The ratio was used for estimating expected numbers of cancers in 1988-2019, and 1995-2019.

RESULTS

From 1995 to 2019, 506,607 non-invasive and invasive breast cancers were diagnosed among women aged 50-64 years (1995-2001) and 50-70 years (2002-2019). A first method estimated that 95,297 cancers were in excess to the number of cancers that would be expected had the NHSBSP not existed. 42,567 screen-detected non-invasive and micro-invasive cancers represented 45.8% of the total excess cancer. 18.8% of all cancers diagnosed among women invited to screening, 25.1% of cancers found in women attending screening, and 35.1% of cancers detected by screening would represent overdiagnosis. A second method estimated that, 18.0% of all cancers diagnosed in 1988-2019, and 18.2% of all cancers diagnosed in 1995-2019 among women invited to screening would represent overdiagnosis.

CONCLUSION

The two independent methods obtained similar estimates of overdiagnosis. The NHS Breast Screening Programme in England is associated with substantial amount of overdiagnosis.