There were 9 RCTs and 4 case-control studies.
Women aged 40 to 74 years:
RR of breast cancer death among women who underwent screening mammography, compared to those who did not, was 0.75 (95% confidence interval, CI: 0.68, 0.83).
Comparison of patients in the RCTs revealed there was no difference in outcome when various screening techniques, screening intervals or inclusion of clinical breast examination were taken into consideration.
Number of mammographic views:
single view, RR 0.76 (95% CI: 0.64, 0.9); two views, RR 0.80 (95% CI: 0.70, 0.92).
Screening interval:
12 months, RR 0.77 (95% CI: 0.64, 0.90); 18 to 33 months, RR 0.79 (95% CI: 0.70, 0.89).
Clinical breast examination included with screening:
yes, RR 0.79 (95% CI: 0.67, 0.95); no, RR 0.78 (95% CI: 0.68, 0.89).
Results were similar when duration of follow-up, duration of screening and study start date (pre- or post-1980) were considered.
Women aged 50 to 74 years:
Results from 10 (8 RCTs and 2 case-control) of the 13 identified trials showed a RR of mortality from breast cancer of 0.74 (95% CI: 0.66, 0.83) in the screened group.
Number of mammographic views: one view mammography appeared to have sufficient sensitivity to reduce breast cancer mortality in this group of women. Single view, RR 0.70 (95% CI: 0.58, 0.84); two view, RR 0.83 (95% CI: 0.71, 0.97).
Screening interval: screening every 18 to 33 months, or every 12 months, resulted in 23% reduction in breast cancer mortality.
Clinical breast examination: clinical examination did not decrease breast cancer mortality beyond the reduction achieved by mammography alone.
Women aged 40 to 49 years:
results in 9 (8 RCTs and 1 case-control) of the 13 identified trials showed a RR of mortality from breast cancer of 0.93 (95% CI 0.76, 1.13) in the screened group.
Number of mammographic views:
single view mammography RR 1.02 (95% CI 0.73, 1.44); two view, RR 0.87 (95% CI ; 0.68, 1.12).
Follow-up:
in those followed for 7 to 9 years there was a non-significant increase in mortality of 2% (95% CI -18%,27%), RR 1.02 (95% CI 0.82, 1.27); in those followed for 10 to 12 years there was a non significant mortality reduction of 17% (95% CI: -35, 6), RR 0.83 (95% CI: 0.65, 1.06).
Overall mortality reduction for 7-12 years is 7% (95% CI -24%,13%).
Screening interval: results are based on the fact that only 2 studies (that were heterogeneous X2 =0.09) screened patients every 12 months. The comparison of these studies with those using longer intervals (12 to 33 months) did not show a difference in breast cancer mortality.
No differences were shown in the overall analysis or the age-specific analysis in relation to duration of screening, clinical breast examination or start date of the study.