ArticlesUse of a decision aid including information on overdetection to support informed choice about breast cancer screening: a randomised controlled trial
Introduction
Mammography screening can reduce a woman's risk of dying from breast cancer but entails the risk of having a cancer diagnosed and treated that would not have presented clinically in her lifetime—termed overdetection or overdiagnosis. Such a diagnosis, and the resulting overtreatment, can harm women physically and emotionally,1 for example, via increased risk of ischaemic heart disease after radiotherapy2 or the psychosocial outcomes of labelling.3
The growth in attention about overdetection has highlighted the importance of ensuring that healthy women invited to breast screening are informed clearly about the potential for both benefit and harm.4, 5 After a review of the evidence, the Independent UK Panel on Breast Cancer Screening wrote that “information should be made available in a transparent and objective way to women invited to screening so that they can make informed decisions”.6 Momentum is shifting from uninformative and persuasive approaches to screening communication7 to clear and balanced information, giving people the opportunity to make informed choices based on their assessment of the trade-offs between potential outcomes.8, 9 A health system centred around the individual should facilitate decision making that incorporates personal values and preferences, irrespective of whether the eventual choice is to screen or not.10 In turn, key performance indicators for screening should reflect informed choice rather than participation.9, 11, 12
Despite calls for better information about overdetection of disease for women invited to breast screening, few studies have reported public responses to this issue. In qualitative studies, women who were eligible for screening were unaware of overdetection but could understand the idea, placed value on information, and thought that making an informed decision was important.13, 14 As far as we know, no randomised trial has addressed whether information about overdetection can improve the quality of women's decisions about undergoing breast screening.
Decision aids communicate evidence-based information on benefits and harms of different health-care options to help people make informed decisions. Findings of randomised trials show that decision aids improve knowledge and facilitate informed choice in various settings,15 including cancer screening.16, 17 In breast screening, however, decision aids have not addressed overdetection comprehensively. In one study,16 a mammography decision aid was assessed in which information about overdetection was placed in an appendix, the frequency of overdetection was not stated, and the decision aid was designed for 70-year-old women deciding whether to continue screening. High-quality evidence is needed to show how information about the concept and frequency of overdetection affects decision making in women approaching age 50 years (when screening is initiated in many countries).
We developed two versions of a decision aid (intervention and control) giving explanatory and quantitative information about important breast-screening outcomes (panel 1).18 Both versions included information about breast cancer deaths averted and false positives from screening, whereas the intervention decision aid also contained data for overdetection. Levels of benefit and overdetection were derived from a meta-analysis of screening trials by the Independent UK Panel on Breast Cancer Screening.6 Although diverse estimates of overdetection are available, derived from various data and methods, randomised trials provide the best evidence for the extent of overdetection.6, 8
Our resources were designed to support women to make informed choices, not to push them towards or away from screening.7 Decision aids are provided in situations with no obviously right or wrong option, so the focus in evaluating them should not be on the option selected23 but rather on decision quality, defined in terms of knowledge and agreement between values and choice.24 Screening rates might not reflect people's informed decisions if coercion or obstacles are present.12 The aim of our study was to investigate whether evidence-based consumer-friendly information on overdetection improves the level of informed choice about screening in a community sample of women around the target age for starting breast screening in Australia.
Section snippets
Study design and participants
We did a community-based parallel-group, randomised controlled trial in New South Wales (NSW), Australia. The NSW Electoral Commission extracted from the electoral register a random cohort of women aged 48–50 years. Trained interviewers from an independent non-profit company telephoned potential respondents to ascertain their eligibility. Exclusion criteria were: mammography in the past 2 years; a personal history of breast cancer; increased risk of breast cancer compared with the population
Results
From January, 2014, to July, 2014, 2647 women aged 48–50 years were contacted by an independent non-profit company about the study; of these, 1255 individuals were eligible. 1061 (85%) women gave informed consent and were sent the standard NSW screening programme leaflet.27 The baseline interview was not completed for 119 women, who were excluded. 942 participants were randomly allocated to receive either the intervention or control decision aid, including 63 women who were chosen at random for
Discussion
Our study findings show that a decision aid containing explanatory and quantitative information on overdetection increased knowledge and enabled more women to make an informed choice about breast screening, compared with a control decision aid with overdetection information omitted. The decision aid did not adversely affect women by raising decisional conflict, anxiety, or worry. Our findings also indicated that some women, when better informed about the balance of harm and benefit, can make
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