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Benefits of the NHS breast screening programme outweigh small risk of overdiagnosis

Breast screening x-ray images

Published: 19 July 2022

New research funded by NIHR has estimated that the NHS breast screening programme has low rates of overdiagnosis, when screening detects very slow-growing cancers that would never have gone on to cause symptoms.

Despite the benefits of breast screening in diagnosing cancers at an earlier stage when they are easier to treat, there is a risk of harm if women are treated unnecessarily for cancers that are extremely slow-growing and would never have caused any problems during a woman’s lifetime. Treatments like surgery and radiotherapy can have serious side effects, and when a cancer is diagnosed it is impossible to tell how fast it will grow, so all cancers need treatment.

The new study, funded by NIHR’s Policy Research Programme and led by researchers at Queen Mary University of London, analysed 57,493 cases of breast cancer diagnosed in 2010 or 2011, and matched them with 105,653 controls.

The researchers calculated how many cancers were diagnosed through the screening programme in women aged 50-77 who attended three-yearly screening, and compared this with the number of cancers diagnosed in women who did not attend screening but were in the same age category, including seven years beyond the upper age limit for screening. The extra cases diagnosed in the women who attended screening were used as an estimate for how many cancers are overdiagnosed.

The estimated number of cases of overdiagnosis in women attending all screening in the programme was just under 3 per 1000. This corresponded to an estimated 3.7% of cancers detected through screening being overdiagnosed.

This is lower than has been suggested by previous research, where estimates of overdiagnosis have ranged from less than 5% to more than 30%. The researchers conclude that the breast screening programme in England is associated, at worst, with modest overdiagnosis of breast cancer.

Professor Stephen Duffy, joint lead investigator, 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.”

Find out more about this research on the Queen Mary University of London website, or read the research paper in the journal Cancer Medicine.


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