If we assume that screening reduces breast cancer mortality by 15% and that overdiagnosis and overtreatment is at 30%, it means that for every 2000 women invited for screening throughout 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress including anxiety and uncertainty for years because of false positive findings. To help ensure that the women are fully informed before they decide whether or not to attend screening, we have written an evidence-based leaflet for lay people that is available in several languages on www.cochrane.dk. Because of substantial advances in treatment and greater breast cancer awareness since the trials were carried out, it is likely that the absolute effect of screening today is smaller than in the trials. Recent observational studies show more overdiagnosis than in the trials and very little or no reduction in the incidence of advanced cancers with screening.
False-positive results in the randomized controlled trial of mammographic screening from age 40 ("Age" trial).
False-positive recall is a recognized disadvantage of mammographic breast screening, and the rate of such recalls may be higher in younger women, potentially limiting the value of screening below age 50.
                Attendance and screening outcome data for 53,884 women in the intervention arm of the U.K. Age trial were analyzed to report observed false-positive recall rates during 13 years of trial fieldwork. The Age trial was a randomized controlled trial of the effect of mammographic screening from age 40 on breast cancer mortality, conducted in 23 National Health Service screening centers between 1991 and 2004. Women randomized to the intervention arm were offered annual invitation to mammography from age 40 or 41 to age 48.
                Overall, 7,893 women (14.6% of women the intervention arm and 18.1% of women attending at least one routine screen) experienced one or more false-positive screen during the trial. The rates of false-positive mammography at first and subsequent routine screens were 4.9% and 3.2%, respectively. The cumulative false-positive rate over seven screens was 20.5%. Eighty-nine percent of women who had a false-positive recall at their previous screen attended their next invitation to routine screening.
                The rates of false-positive recall in the Age trial were comparable with the national screening program; however, the positive predictive value of referral was lower. Experiencing a false-positive screen did not seem to lessen the likelihood of re-attendance in the trial.
                The question of greatly increased false-positive rates in this age group and of their compromising re-attendance is refuted by the findings of this study.
                ©2010 AACR.