We assessed changes in advanced cancer incidence and cancer mortality in eight randomized trials of breast cancer screening.
Depending on published data, advanced cancer was defined as cancer > or = 20 mm in size (four trials), stage II+ (four trials), and > or = one positive lymph node (one trial). For each trial, we obtained the estimated relative risk (RR) and 95% CI between the intervention and control groups, for both breast cancer mortality and diagnosis of advanced breast cancer. Using a meta-regression approach, log(RR-mortality) was regressed on log(RR-advanced cancer), weighting each trial by the reciprocal of the square of the standard error of log(RR) for mortality.
RR for advanced breast cancer ranged from 0.69 (95% CI, 0.61 to 0.78) in the Swedish Two-County Trial to 0.97 (95% CI, 0.97 to 1.25) in the Canadian National Breast Screening Study-1 (NBSS-1) trial. Log(RR)s for advanced cancer were highly predictive of log(RR)s for mortality (R(2) = 0.95; P