Screening for breast cancer detects tumours at an earlier biological stage.

Between August 1988 and July 1990, 17,678 women in the Gateshead, Sunderland, South Tyneside and Durham districts attended the national breast screening programme. A total of 131 cancers were detected. The morphology of cancers detected by screening was compared with that of tumours in 71 patients presenting clinically in the same period. Screen-detected cancers included a higher proportion of tumours of more favourable histological grade and type, were smaller in size and had less axillary lymph node involvement than those detected clinically. Survival was predicted from the Nottingham Prognostic Index. Patients with screen-detected cancer had an expected survival advantage (95 per cent confidence interval) of 26.5 (12.3-40.6) per cent at 5 years, 26.5 (11.8-41.2) per cent at 10 years and 29.1 (14.5-43.7) per cent at 15 years. This survival advantage in screened patients expected at 5, 10 and 15 years is consistent with the 30 per cent reduction in mortality rate demonstrated in the Health Insurance Plan study and the Swedish two counties trial.