NHS Breast Screening ProgrammeNHSBSP Publication No. 61. Feb 2006www.cancerscreening.nhs.uk • NHS Breast Screening Programme (NHSBSP) began in 1988 • Aims to invite all women aged 50-70 years once every 3 years • Number of breast cancer registrations has increased by almost 50% since NHSBSP began • Cancers detected by screening are smaller and mastectomy is less likely • NHSBSP plus earlier symptomatic presentation and greater use of adjuvant therapy has reduced mortality from breast cancer • Mammography screening trials show a 25% relative risk reduction in mortality (ITT), equates to 35% in women regularly screened • NHSBSP saves an estimated 1400 lives each year in England.
Benefits vs. harms of screeningNHSBSP Publication No. 61. Feb 2006 • About 1 in 400 women regularly screened over a 10 year period will be prevented from dying from breast cancer • About 1 in 8 women regularly screened will be recalled for further tests over a 10-year period • Breast cancer will be diagnosed in only a few of these • Delicate balance between reducing recall rates so far that small cancers are missed and calling back too many women causing anxiety and possibly reducing re-attendance • Among women routinely screened and diagnosed with breast cancer: • 1 in 8 fewer women will die than would have done if they’d not been screened • 1 in 8 spared mastectomy • 1 in 8 women have a cancer detected (and treated) which would not have affected her had she not been screened.
NHSBSP Publication No. 61. Feb 2006 Positive predictive value (PPV) of abnormal mammogram = 19% i.e. 19% of people with abnormal mammogram have breast cancer
Overdiagnosis in breast cancer screening (1)Jorgensen KJ, Gøtzsche PC. BMJ 2009;339:b2587Welch HG. BMJ 2009;339:b1425; MeReC Rapid Review Blog No. 417 • From meta-analysis, the total overdiagnosis of breast cancer in publicly available mammography screening programmes was estimated as 52% (95%CI 46% to 58%) i.e. about one in three cancers is overdiagnosed • For every 1000 women (>50 years) who are screened for breast cancer annually for 10 years: • 1 woman will avoid dying from breast cancer • 2 to 10 women will be overdiagnosed and treated needlessly • 10 to 15 women will be told they have breast cancer earlier than they would otherwise have been told, but this will not affect their prognosis • 100 to 500 women will have at least one ‘false alarm’ (approximately half these women will undergo a biopsy). The absolute risks and benefits of breast cancer screening, including the level of overdiagnosis, should be communicated to women in a balanced way so they can make an informed decision to have screening or not.
Overdiagnosis in breast cancer screening (2)Welch HG. BMJ 2009;339:b1425 ‘Mammography is one of medicine’s ‘close calls’ — a delicate balance between benefits and harms — where different people in the same situation might reasonably make different choices.’ ‘Mammography undoubtedly helps some women but hurts others. No right answer exists, instead it is a personal choice.’
Summary • Breast cancer screening contributes to the falling mortality from the disease • About 1 in 400 women regularly screened over a 10-year period will be prevented from dying from breast cancer • 1 in 8 women diagnosed with breast cancer avoids a mastectomy she would have needed, had she not had the cancer diagnosed by screening • The benefits must be weighed against the harms • About 1 in 8 women regularly screened will be recalled for further assessment over a 10-year period, but very few of these have the disease • 1 in 8 women screened and diagnosed have a cancer which would not have affected her had she not been screened.