Screening for breast cancer
Eight eligible trials were identified.We excluded a biased trial and included 600,000 women in the analyses. Three trials with adequate randomisation did not show a significant reduction in breast cancer mortality at 13 years (relative risk (RR) 0.90, 95% confidence interval (CI) 0.79 to 1.02); four trials with suboptimal randomisation showed a significant reduction in breast cancer mortality with an RR of 0.75 (95% CI 0.67 to 0.83). The RR for all seven trials combined was 0.81 (95% CI 0.74 to 0.87).
We found that breast cancer mortality was an unreliable outcome that was biased in favour of screening, mainly because of differential misclassification of cause of death. The trials with adequate randomisation did not find an effect of screening on cancer mortality, including breast cancer, after 10 years (RR 1.02, 95% CI 0.95 to 1.10) or on all-cause mortality after 13 years (RR 0.99, 95% CI 0.95 to 1.03).
Numbers of lumpectomies and mastectomies were significantly larger in the screened groups (RR 1.31, 95% CI 1.22 to 1.42) for the two adequately randomised trials that measured this outcome; the use of radiotherapy was similarly increased.
Screening is likely to reduce breast cancer mortality. As the effect was lowest in the adequately randomised trials, a reasonable estimate is a 15% reduction corresponding to an absolute risk reduction of 0.05%. Screening led to 30% overdiagnosis and overtreatment, or an absolute risk increase of 0.5%. This means that for every 2000 women invited for screening throughout 10 years, one will have her life prolonged and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress for many months because of false positive findings. It is thus not clear whether screening does more good than harm.”
From this review by Gøtzsche and Nielsen from The Nordic Cochrane Centre. Here’s a relatively recent press release from Cochrane (in Danish). Here’s a related article published a few days ago. By now, it seems that Gøtzsche thinks it is quite clear whether screening does more good than harm:
“I believe the time has come to realise that breast cancer screening programmes can no longer be justified,” Gøtzsche said.”
Maybe there’s a way to modify the current screening programmes somewhat so that they include mainly/only relatively high-risk subpopulations – but identifying just who the high-risk individuals are is never easy, which is part of why screening programmes like these are undertaken in the first place. Either way, if the results reported above are ‘in the right ballpark’ a serious cost/benefit analysis should in my mind lead to a rejection of the current programme(s).
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