Seven RCTs (11,089 women in the intervention groups and 98,357 in the control groups) and 6 meta-analyses were included.
All the RCTs were included in at least one of the meta-analyses. Twelve studies assessed the psychological effects of screening, most of which were included in a single review that was also included.
Most of the trials lacked the power to exclude a potentially significant difference. Only one RCT was designed specifically for women aged 40 to 49 years; other results were from a post-hoc subgroup analysis. The relative risks from death cancer reported in RCTS of screening mammography among women aged 40 to 49 years ranged from 0.6 to 11. All but two of the confidence intervals (CIs) for these estimates included 1. The numbers-needed-to-screen to avoid one death from breast cancer were 500 and 782 in the trials that reported statistically significant relative risks at the 5% level.
The pooled relative risks ranged from 0.82 to 1.04; only two of these were statistically significant at the 5% level. Only one meta-analysis included all the trials of breast cancer screening. This meta-analysis reported a relative risk of 0.82 (95% CI: 0.71, 0.95), suggesting strong evidence in favour of a benefit of screening. It also reported a number-needed-to-screen of 1,540 to avoid one death from breast cancer.
The most recent meta-analysis included only 1.5 of the 7 trials, as it judged that randomisation in the other trials had been inadequate. This review was therefore dominated by the negative findings from one of the included trials, and it reported a relative risk of 1.04 (95% CI: 0.84, 1.27).
Other effects of screening.
One RCT reported that over 10 years of screening, 12.6% of younger women required additional mammograms and 0.56% of biopsies showed benign lesions. A second trial reported that 2.5% of women were called back, 0.9% had biopsies, 0.1% had surgery that revealed benign disease, and that about 2 to 3 operations were performed for every death prevented.
Psychological effects of screening.
Women had less anxiety and depression on the day of screening than at baseline. Lower age was associated with increased anxiety. Increased emotional and physical dysfunction was seen only in women recalled for additional testing and was resolved over time. Psychological distress decreased with time in women with normal or false-positive mammograms, or negative biopsy results, but it increased in women found to have cancer. A retrospective survey reported that 72% of women felt reassured by screening. Less information was available on false-negative results.