On the benefits and harms of screening for breast cancer

claim that our critique of the randomized screening trials has little merit; that there is no reason to believe that the Canadian study was of better quality than the New York Health Insurance Plan (HIP) study or the Two-County study; and that the prior consensus on mammography was correct. However, their review suffers from erroneous assumptions and biased statistical analyses, and their quotations are often selective and misleading. In my discussion of the issues, I will follow when possible the sequence of arguments used by FPR. FPR claim in their abstract that early detection leads to less invasive therapy. This could have been true, if the only effect of screening had been to detect the same tumours earlier that are detected later if women are not screened. FPR naively believe that screening does just that, i.e. does not lead to overdiagnosis. They note, for example, that the incidence of breast cancers in the New York HIP study is the same in the control group as in the screening group 5–7 years after screening started (their table 2), as they expected. I will explain under the HIP study below why this argument is faulty. The level of overdiagnosis can be studied reliably in the trials from Canada and Malmö which did not differentially exclude women with prior breast cancer after randomization and did not introduce early, systematic screening of the whole control group. 2–4 There was an overdiagnosis of 30% 5,6 which corresponds closely to the 31% excess surgery we have previously described 2,3 (Table 1). A similar result was seen for the trials that screened the whole control group when only cancers before this screen were included 7–9 (Table 2). The excess surgery rate was 20% for mastectomies. 2,3 We have discussed in detail why it is likely that even today, there would be about 20% more mastectomies when women are screened than if they are not screened. 3 In Southeast Netherlands, for example, when screening was introduced from 1990 to 1998, the number of women who underwent breast-conserving surgery increased by 71%, and the number of women who underwent mastectomy increased by 84%. 10 If the study had included carcinoma in situ there would have been even more mastectomies. 3,11 A study from Italy claimed that screening had not led to an increase in mastectomies, 12 but this study had no control group and the premises for the study …