Women who understand the risk of over-detection and over-diagnosis associated with mammography screening have lower intentions of undergoing breast screening, according to a new Lancet study (2015; doi:10.1016/S0140-6736(15)60123-4).

“Mammography screening can reduce breast cancer deaths, but most women are unaware that inconsequential disease can also be detected by screening, leading to over-diagnosis and overtreatment,” said study author Professor Kirsten McCaffery, PhD, of the University of Sydney in Australia.

Over-detection and over-diagnosis refers to the diagnosis and treatment of breast cancer that would not have presented clinically during a woman’s lifetime. Such a diagnosis, and the resulting overtreatment, can harm women physically and emotionally.

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McCaffery said that this first of its kind study underlines the ethical imperative to provide women with clear decision-support materials so they can make more informed decisions about whether to undergo breast screening mammography. A health system centered around the patient should assist decision-making in a way that it incorporates a woman’s values and preferences, irrespective of her eventual choice to undergo screening or not.

McCaffery added that “momentum is shifting from uninformative and persuasive approaches to screening communication to clear and balanced information, giving people the opportunity to make informed choices based on their assessment of the trade-offs between potential outcomes.”

The study is the first research to assess the effect of including over-detection information in decision support materials for women ages 48 to 50 years who are on the threshold of becoming candidates for mammography screening.

The 879 women who participated in the randomized, controlled study had not had mammography in the past 2 years and did not have a personal or strong family history of breast cancer.

Compared to controls, for women who were provided with decision support that contained explanatory and quantitative information about over-detection, significantly more women had adequate knowledge about breast cancer screening and made an informed choice whether to be screened.

Also, these informed women had significantly less favorable attitudes towards breast cancer screening, although attitudes remained positive overall. Finally, significantly fewer of these women intended to be screened for breast cancer.

The intervention decision aid contained evidence-based information about important outcomes of breast screening over 20 years, compared with no screening. The information covered breast cancer mortality reduction, over-detection, and false positives. The control version omitted all content about over-detection but was otherwise identical to the intervention decision aid.

Quantitative evidence included in the decision aids was taken from an updated version of a published model of mammography screening outcomes for women in Australia.

The model incorporates estimates of both over-detection and the reduction in breast cancer mortality from screening, which were derived from a meta-analysis of randomized trial data and adjusted to account for the effect of regularly undergoing screening.

These estimates were applied to current Australian data for incidence and mortality to quantify cumulative outcomes of biennial screening from age 50 years to 69 years versus no screening over this period.