Women are surprised and shocked that breast screening can lead to ‘overdiagnosis’ of cancer, but would rather go for screening than take the risk of missing a cancer that could be treated, according to new research published in BMJ Open.
The Cancer Research UK funded study carried out focus groups with 40 women1 aged between 50 and 71 years old based in and around London, including both women who had already been screened and others who had not attended for screening.
The researchers gave participants information on breast screening and the possibility that a proportion of slower-growing cancers diagnosed through screening may never have caused a problem in a woman’s lifetime – known as ‘overdiagnosis’. Participants were invited to discuss the information.
They found that women were initially surprised and shocked to discover that breast screening could result in cancers being found that might not ever have needed treatment. However, most of them remained positive towards breast screening – often noting that they preferred the risk of over-treatment and side-effects to that of under-treatment2.
The study found that many women struggled to understand the concept of overdiagnosis, and often took the view that rather than affecting their decision about whether or not to go for screening, it was mainly an issue for treatment decisions.
Dr Jo Waller, a Cancer Research UK scientist at UCL and study author said: “Our research is the first of its kind to look at the attitudes of British women towards overdiagnosis in breast screening.
“We found a widespread lack of awareness of overdiagnosis and a strong view that the information was important, although it rarely changed women’s beliefs about the value of screening or their decisions about attending in the future.
“Our study also highlighted the difficulty of communicating risk information about cancer screening. Population-level data and statistical modelling are difficult even for medical experts to understand, and more so for individuals to use to weigh up the personal pros and cons of screening.”
The study follows on from the Independent Breast Screening Review, commissioned by Cancer Research UK and the Department of Health in October 2012 which aimed to give definitive answers to the benefits and risks of breast cancer screening3.
The review concluded that breast screening extends lives through early detection and treatment but at a cost of overdiagnosis; which was estimated to be around three cases of overtreatment for every death prevented although there was a high degree of uncertainty around the specific numbers.
Sara Hiom, director of early diagnosis at Cancer Research UK, said: “We think it’s important for women to have access to clear information about breast screening, the balance of benefits and harms and the fact that they could be diagnosed with and treated for a cancer that might not cause them harm.
“Overdiagnosis happens because some breast cancers grow so slowly that it would take more than a lifetime for them to spread around the body and threaten a woman’s health. The term ‘overtreatment’ is used to acknowledge that some cancers are treated that did not need to be, but it’s not currently possible for doctors to distinguish such cancers from those needing treatment, either at the time or later.
“So, while this study highlights the need for clearer communication about overdiagnosis, it also demonstrates the need for more research to identify women at higher risk of breast cancer and distinguish between faster and slower growing cancers. We are working towards this now.
“Cancer Research UK continues to recommend that women go for breast screening when invited.”
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Waller, J et al, Women’s responses to information about overdiagnosis in the UK breast screening programme: a qualitive study (2013) BMJ Open, DOI:10.1136/bmjopen-2013-002703
1 Six focus groups were conducted with women living in and around London in the mammography screening age range (50-71) to explore their existing knowledge and experience of overdiagnosis. All women spoke fluent English, none had a personal history of cancer, and none worked in occupations related to cancer or cancer screening.
2 Further information consisted of a statement on overdiagnosis read aloud to the participants during the group discussion: “It’s been suggested that some of the breast cancers that get diagnosed through breast screening are so slow-growing that they would not have caused any problems. But because we can’t yet tell which kind of cancer is the slow-growing kind, the woman receives the usual treatment for breast cancer (e.g. surgery). Of all women who go for breast screening, about 8 in 1000 are diagnosed with cancer. It’s very hard to know what proportion of cancers diagnosed in the screening programme are of the slow-growing type and the experts disagree at the moment. The estimates have varied from 1 in 8 of women who are diagnosed to 3 in 8.”
3 Independent UK Panel on Breast Cancer Screening, The benefits and harms of breast cancer screening: an independent review (2012) The Lancet, DOI:10.1016/S0140-6736(12)61611-0