NHS Breast Screening Programme in England shows little evidence of overdiagnosis
The NHS Breast Screening Programme in England has shown little, if any, evidence of overdiagnosis, according to a new NIHR-funded study.
Cases of breast cancer in UK women have increased by 4% in the last decade, but breast cancer deaths are declining, in part due to early diagnosis through the NHS Breast Screening Programme, which invites women aged 50-70 for mammographic screening every three years. Despite the benefits of screening, there has remained debate over the potential harms of overdiagnosis, the detection of a slow growing cancer that would never cause symptoms. Estimates of overdiagnosis have varied widely, from <5% of screen detected cancers to more than 30%.
To quantify overdiagnosis in the NHS Breast Screening Programme, researchers undertook a study of 57,493 breast cancer cases diagnosed in 2010 or 2011, matched with 105,653 controls. They estimated the effect of screening on breast cancer risk, and the results were combined with national incidence data to estimate absolute rates of overdiagnosis. Overdiagnosis was calculated as the cumulative excess of cancers diagnosed in women aged 50-77 attending three-yearly screening between ages 50 and 70 compared with women attending no screens.
The estimated number of cases of overdiagnosis in women attending all screens in the programme was just under 3 per 1000, corresponding to an estimated 3.7% of screen detected cancers overdiagnosed and considerably lower than has been suggested in the past. Authors conclude that the NHS Breast Screening Programme is associated, at worst, with modest overdiagnosis of breast cancer.
WIPH Professor of Cancer Screening and joint lead investigator, Stephen Duffy, said: “These results provide some reassurance that participation in the NHS Breast Screening Programme confers only a low risk of an overdiagnosed breast cancer. Along with the results of our previous study of the effect of screening on breast cancer mortality, this indicates that the benefit of screening in preventing deaths from breast cancer outweighs the small risk of overdiagnosis.”
A case-control study to evaluate the impact of the breast screening programme on breast cancer incidence in England. Oleg Blyuss, Amanda Dibden, Nathalie J Massat, Dharmishta Parmar, Jack Cuzick, Stephen W Duffy and Peter Sasieni. Cancer Medicine 2022.