BREAST-CANCER SCREENING WITH MAMMOGRAPHY - OVERVIEW OF SWEDISH RANDOMIZED TRIALS

Despite encouraging results from screening trials the efficacy of mamm ography in reducing mortality remains somewhat controversial. Five stu dies have been done in Sweden. This overview, based on 282 777 women f ollowed for 5-13 years in randomised trials in Malmo, Kopparberg, Oste rgotland, Stockholm, and Gothenburg, reveals a 24% (95% confidence int erval 13-34%) significant reduction of breast cancer mortality among t hose invited to mammography screening compared with those not invited. To avoid the potential risk of differential misclassification causes of death were assessed by an independent end-point committee after a b linded review of all fatal breast cancer cases. The mortality reductio n was similar, irrespective of the end-point used for evaluation (''br east cancer as underlying cause of death'' or ''breast cancer present at death''). There was a consistent risk reduction associated with scr eening in all studies, although the point estimate of the relative ris k for all ages varied non-significantly between 0.68 and 0.84. The cum ulative breast cancer mortality by time since randomisation was estima ted at 1.3 per 1000 within 6 years in the invited group compared with 1.6 in the control group. The corresponding figures after 9 years are 2.6 and 3.3 and after 12 years 3.9 and 5.1. The largest reduction of b reast cancer mortality (29%) was observed among women aged 50-69 at ra ndomisation. Among women 40-49 there was a non-significant 13% reducti on. In this younger age group cumulative breast cancer mortality was s imilar in the invited and control group during the first 8 years of fo llow-up. After 8 years there was a difference in favour of the invited women. There was no evidence of any detrimental effect of screening i n terms of breast cancer mortality in any age group. Among women aged 70-74 years screening seems to have had only a marginal impact.