Is screening for breast cancer with mammography justifiable?

Background A 1999 study found no decrease in breast-cancer mortality in Swe den, where screening has been recommended since 1985. We therefore reviewed the methodological quality of the mammography trials and an influential Sw edish meta-analysis, and did a meta-analysis ourselves. Methods We searched the Cochrane Library for trials and asked the investiga tors for further details. Meta-analyses were done with Review Manager (vers ion 4.0). Findings Baseline imbalances were shown for six of the eight identified tri als, and inconsistencies in the number of women randomised were found in fo ur. The two adequately randomised trials found no effect of screening on br east-cancer mortality (pooled relative risk 1.04 [95% CI 0.84-1.27]) or on total mortality (0.99 [0.94-1.05]). The pooled relative risk for breast-can cer mortality for the other trials was 0.75 (0.67-0.83), which was signific antly different (p=0.005) from that for the unbiased trials. The Swedish me ta-analysis showed a decrease in breast-cancer mortality but also an increa se in total mortality (1.06 [1.04-1.08]); this increase disappeared after a djustment for an imbalance in age. Interpretation Screening for breast cancer with mammography is unjustified. If the Swedish trials are judged to be unbiased, the data show that for ev ery 1000 women screened biennially throughout 12 years, one breast-cancer d eath is avoided whereas the total number of deaths is increased by six. If the Swedish trials (apart from the Malmo trial) are judged to be biased, th ere is no reliable evidence that screening decreases breast-cancer mortalit y.