Effect of NHS breast screening programme on mortality from breast cancer in England and Wales, 1990-8: comparison of observed with predicted mortality

Objective To assess the impact of the NHS breast screening programme on mor tality from breast cancer in women aged 55-69 years over the period 1990-8. Design Age cohort model with data for 1971-89 used to predict mortality for 1990-8 with assumption of no major effect from screening or improvements i n treatment until after 1989. Effect of screening and other factors on mort ality estimated by comparing three year moving averages of observed mortali ty with those predicted (by five year age groups from 50-54 to 75-79), the effect of screening being restricted to certain age groups. Setting England and Wales. Subjects Women aged 40 to 79 years. Results Compared with predicted mortality in the absence of screening or ot her effects the total reduction in mortality from breast cancer in 1998 in women aged 55-69 was estimated as 21.3%. Direct effect of screening was est imated as 6.4% (range of estimates from 5.4-11.8%). Effect of all other fac tors (improved treatment with tamoxifen and chemotherapy, and earlier prese ntation outside the screening programme) was estimated as 14.9% (range 12.2 -14.9%). Conclusions By 1998 both screening and other factors, including improvement s in treatment, had resulted in substantial reductions in mortality from br east cancer. Many deaths in the 1990s will be of women diagnosed in the 198 0s and early 1990s, before invitation to screening. Further major effects f rom screening and treatment are expected, which together with cohort effect s should result in further substantial reductions in mortality from breast cancer, particularly for women aged 55-69, over die next 10 years.