Information on overdetection of breast cancer provided within a decision aid increased the number of women making an informed choice about breast screening. Becoming better informed might mean women are less likely to choose screening.
—Jolyn Hersch, MApplSc, Kirsten McCaffery, PhD, and colleagues
In a study reported in Lancet, Jolyn Hersch, MApplSc, of the University of Sydney, and colleagues found that use of a decision aid containing information on overdetection in breast cancer screening was associated with an increased rate of informed choice regarding screening, a reduced rate of positive attitudes toward screening, and reduced intention to be screened compared with use of a decision aid not including such information.1 Kirsten McCaffery, PhD, of the University of Sydney, is the corresponding author of the Lancet article.
In the community-based trial conducted in New South Wales, Australia, 879 women aged 48 to 50 years who had not had mammography in the past 2 years and did not have a personal or strong family history of breast cancer were randomized between January 2014 and July 2014 to receive an intervention decision aid including evidence-based explanatory and quantitative information on overdetection, breast cancer mortality reduction, and false-positive results (n = 440) or a control decision aid including information on breast cancer mortality reduction and false-positive results (n = 439).
The intervention decision aid contained evidence-based information about outcomes of breast screening vs no screening over a period of 20 years, including information on breast cancer mortality reduction, overdetection, and false-positive results. The control version was identical except for exclusion of all content about overdetection.
The quantitative evidence included in the decision aids was from a model of mammography screening outcomes for women in Australia; estimates of overdetection and reduction in breast cancer mortality associated with screening were derived from a meta-analysis of randomized trial data and adjusted to account for the effect of regular screening rather than ‘invitation to be screened.’ The estimates were applied to current Australian data for incidence and mortality to provide quantitative cumulative outcomes with biennial screening vs no screening from ages 50 to 69 years. The 20-year cumulative likelihood of a false-positive result (including the number of women screened with a false-positive result and the number having a biopsy) was modeled from current Australian data.
The primary outcome was informed choice about breast screening, defined as adequate knowledge and consistency between attitudes and screening intentions. Participants answered questions regarding knowledge, attitudes, and intentions about screening and were considered to have made an informed choice if they had adequate knowledge, based on predefined subscale scores, and if attitudes and intentions were consistent (ie, positive attitudes and intentions or negative attitudes and intentions).
Knowledge was assessed by questions on benefit, false-positive results, and overdetection, with questions on both conceptual knowledge and numerical knowledge. Participants were interviewed via telephone at 3 weeks after randomization. The primary outcome was analyzed in all women who completed all follow-up interview questions.
Among the two cohorts, 21 women in the intervention group and 20 in the control group were lost to follow-up, and 10 and 11 did not answer all interview questions. Among 409 women in the intervention group and 408 in the control group, 99 vs 63 (24% vs 15%, difference = 9%, P = .0017) were considered to have made an informed choice regarding screening. In an analysis including conceptual knowledge but not numerical knowledge, informed choice was made by 50% vs 19% (P < .0001).
Compared with the control group, significantly more women in the intervention group met the predefined threshold for adequate overall knowledge on conceptual and numerical items combined for the benefit, false-positive results, and overdetection subscales (29% vs 17%, P < .0001).
The difference was attributable to better performance of the intervention group on the overdetection subscale. There was no difference between the intervention group and the control group with regard to knowledge about breast cancer mortality benefit (65% vs 61%), better knowledge in the control group regarding false-positive results (58% vs 66%, P = .0154), and better knowledge in the intervention group regarding overdetection (55% vs 27%, P < .0001).
Among 11 individual conceptual items, there were no differences between groups with regard to knowledge reflected in response to “Screening is for women without symptoms” (89% vs 88%), “Screening reduces breast cancer deaths” (93% vs 95%), “Screening will not find every breast cancer” (95% vs 95%), or “Screening may lead to false-positive results” (99% vs 100%). However, more women in the intervention group (all P < .05) had correct responses to the overdetection items of “Screening increases breast cancer diagnoses” (79% vs 73%), overdetection vs false-positive distinction (43% vs 12%), “Not all breast cancers cause illness or death” (68% vs 33%), “Cannot predict whether a cancer will cause harm” (78% vs 61%), “Cancer that might not cause problems is treated” (87% vs 76%), “Some women get treatment they do not need” (75% vs 26%), and “Overdetect more than prevent death” (77% vs 66%).
Attitudes and Intentions
Significantly fewer women in the intervention group expressed positive attitudes toward screening (69% vs 83%, P < .0001), with 24% vs 38% having highly positive attitudes.
Significantly fewer women in the intervention group indicated that they would definitely be screened or were likely to be screened (74% vs 87%, P < .0001); 47% vs 64% indicated they would definitely be screened, 26% vs 23% indicated they were likely to be screened, 16% vs 7% were unsure, and 10% vs 6% indicated they were unlikely to be screened or definitely would not be screened.
The investigators concluded: “Information on overdetection of breast cancer provided within a decision aid increased the number of women making an informed choice about breast screening. Becoming better informed might mean women are less likely to choose screening.” ■
Disclosure: The study was funded by the Australian National Health and Medical Research Council. For full disclosures of the study authors, visit www.thelancet.org.
1. Hersch J, Barratt A, Jansen J, et al: Use of a decision aid including information on overdetection to support informed choice about breast cancer screening: A randomised controlled trial. Lancet. February 18, 2015 (early release online).
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