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| |  Mammographic Screening May Not Be Effective, Study Suggests LONDON, UK -- January 7, 2000 -- A report in this week's issue of The Lancet reaches the conclusion that screening for breast cancer by mammography is not justified. Dr. Peter Gotzsche and Mr. Ole Olsen, of the Nordic Cochrane Centre, Copenhagen, Denmark, reanalysed data from previously published trials and concluded that "there is no reliable evidence that screening decreases breast cancer mortality". They were prompted to look at this issue because a study in Sweden had shown no decrease in breast-cancer mortality since the nationwide screening programme was introduced in that country in 1985. The investigators examined the results from eight trials that randomly assigned women to receive mammographic screening or to be in an unscreened control group. Two of the trials, carried out in Canada and Malmo, Sweden, met widely accepted criteria for an adequate randomisation process, and the women in the two randomly selected groups were similar in terms of characteristics that affect a woman's risk of breast cancer, such as age, family history of breast cancer, previous lumps in the breast, pregnancies, menopause, education, and place of birth. Several of the other six trials (done in Edinburgh, Scotland; New York, USA; and areas of Sweden), however, had inadequate randomisation procedures, and the groups of women compared were not strictly comparable because the groups differed substantially in age or other risk factors. Another problem was that the exact numbers of women in each group were uncertain in four of the trials. Gotzsche and Olsen calculated the effect of screening on breast-cancer mortality separately for the two trials that were adequately randomised and for the other six trials. They found that the evidence from the Canadian and Malmo trials showed no significant effect of screening; the other six trials found that screening decreased the risk of death by about 25 percent. For death from any cause, the latter trials showed a slight increase in risk for screened women, however. Therefore, the investigators conclude that screening is not worthwhile. Those who believe that the Swedish trials (other than the Malmo trial) are unbiased "have to accept from the data that screening for breast cancer with mammography causes more deaths than it saves". On the other hand, if it is assumed that the Swedish trials are biased, there is no reliable evidence to support the efficacy of screening programmes, since the two unbiased trials found no effect. In a commentary on this controversial paper, Dr Harry de Koning from the Rotterdam department of Public Health, The Netherlands, says that"...although the issue focused on by Gotzsche and Olsen is very important, they have disregarded the fact that other factors probably have a more important part in lowering the mortality rate through screening." He reports that breast-cancer mortality in Dutch women aged 60-69 is now falling, though no statistically significant decrease in mortality was expected, or found, during the first 9 years of the screening programme in the Netherlands.
Related Link: The Lancet.
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