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Is screening for breast cancer mammography justifiable PDF Print E-mail
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Saturday, 08 January 2000 00:00
"After heated controversy, there now seems to be general acceptance that the benefit of screening for breast cancer with mammography has been well documented. Large randomized trials, including a total of half a million women, have been carried out in New York, USA; Edinburgh, Scotland; Canada; and Malmö, Koppargberg, Östergöland, Stockholm, and Göteborg in Sweden. A meta-analysis of an update of the five Swedish trials, which used data from individual patients, was particularly influential. It showed that screening lowered mortality from breast cancer by 29% in women aged 50-69 years. The findings of a 1999 epidemiological study were therefore surprising. It found no decrease in breast-cancer mortality in Sweden where screening has been recommended since 1985. The observed decrease in number of deaths from breast cancer was 0.8% (not significant), whereas the expected decrease was 11%. Although this study can be criticized, it raises once again the issue of the reliability of the evidence that screening is effective."

"The imbalance in age at baseline in the Swedish trial is important. Nyström and colleagues reported in a specialist journal that the screened women had an increased risk of death (relative risk 1.05; 15,695 women died of 156,911 in the screening group vs 11,887 of 125,866 in the control group). Nyström and colleagues did not test whether this increased mortality was significant, nor did they give a CI [Confidence Interval]. They argued that because breast-cancer mortality constitutes less than 5% of the total mortality, such an analysis "would require very large cohorts and is therefore impossible in practice." … The effect of screening programmes, if any, is small and the balance between beneficial and harmful effects is very delicate. Unfortunately, the randomization process failed to create similar groups in six of the eight trials of mammographic screening."

"We could not assess psychological morbidity related to false-positive findings because this feature was not reported in the trials. In the USA, Elmore and colleagues estimated the 49% of screened women will experience at least one false-positive mammogram during ten screening rounds and that 19% will be subjected to biopsy. In the Swedish trials, false-positive rates of 4-6% have been reported, corresponding to an average risk of 40% of a false-positive mammogram during ten rounds."

"We conclude that screening for breast cancer with mammography is unjustified."

"On the one hand, those who believe that the Swedish trials are unbiased have to accept from the data that screening for breast cancer with mammography causes more deaths than it saves. The total mortality in the five Swedish trials was 10%, the relative risk of death was 1.06, and the Swedish meta-analysis showed a difference in breast-cancer mortality of 0.1% after 12 years of follow-up. The data therefore show that for every 1000 women screened through 12 years, one breast-cancer death is avoided but the total number of deaths is increased by six. On the other hand, those who believe the Swedish trials (apart from the Malmö trial) are biased have to accept that there is no reliable evidence that screening decreases breast-cancer mortality."

"There is a need for further follow-up of the two unbiased trials and for detailed scrutiny of the other trials to see whether subgroups of women can be identified who have been properly randomized."

Gøtzsche, Peter C and Olsen, Ole, "Is screening for breast cancer mammography justifiable", The Lancet, January 8, 2000, Vol. 355, Num. 0, pp. 129-134


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