Role of mammography screening as a predictor of survival in postmenopausal breast cancer patients.

We examined the effect of population-based screening programme on tumour characteristics by comparing carcinomas diagnosed during the prescreening (N=341) and screening (N=552) periods. We identified screen detected (N=224), interval (N=99) and clinical cancer (N=229) cases. Median tumour size and proportion of axillary lymph node negative cases were 1.5 cm and 65% in the screen detected group, 2.0 cm and 44% in cases found outside the screening, and 3.2 cm and 41% in the cases from the prescreening period. Survival of the breast cancer patients was 66% (95% CI, 60-71%) in the prescreening era group and 73% (95% CI, 66-78%) in the screening era group after 10 years of follow-up. In the screening era group the survival of the screen detected cases was 86% (95% CI, 80-90%) and that of the clinical cancer cases 73% (95% CI, 66-78%) after 10 years. In multivariate analysis the risk of breast cancer death was not significantly different between the prescreening and screening periods (HR 0.82; 95% CI 0.59-1.12, P=0.21). Detection by screening was not an independent prognostic factor in multivariate analysis (HR 0.75; CI 95% 0.50-1.12; P=0.17).