The Nordic Cochrane Centre, Rigshospitalet, Dept 7112, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark. E-mail: p.c.gotzsche{at}cochrane.dk
SirsAlthough I demonstrated that the review by Freedman, Petitti and Robins (FPR) of breast cancer screening1 contains many errors,2 they persist.3
In their review,1 FPR noted that 434 more women with breast cancer prior to randomization were excluded from the study group than from the control group in the Health Insurance Plan (HIP) trial, quoting the principal investigator of this trial. However, in their rejoinder,3 they claim this number originated with me. I wrote that many more women with breast cancer prior to randomization were excluded from the study group than from the control group2 and FPR contradict themselves when they now say my statement is incorrect.3 FPR also say that I withdrew a previous near-retraction. There is no near-retraction in the reference FPR citation4 where I merely restated my concern that retrospective exclusion of women after 18 years of follow-up may not be reliable.
FPR disregard the large discrepancy in the Two-County study involving a benefit of 24% reported by the trialists versus only 10% reported in the Swedish overview.1 Further, although they consulted extensively with the Two-County trialists, they avoid addressing the many discrepancies in numbers of women and deaths reported for this study.1 FPR also turn a blind eye to overdiagnosis,1 though the recent IARC/WHO report on screening acknowledges this is an obvious source of harm.5 The report notes that there was about a 50% increase in breast cancer during 5 years after introduction of screening in Finland and UK and that the rise may be persisting,5 in agreement with our findings and those of others.2
FPR avoid discussing length bias2 and do not acknowledge their error in comparing total mortality among breast cancer cases in the study group versus the control group and then concluding that a significant difference is evidence that screening is effective. It is well-known that case-survival is a highly misleading outcome,6 particularly in screening trials.2,7
Finally, FPR reiterate that it is appropriate to exclude deaths in women who have been invited to screening but refused to get screened. This is not how trials should be analysed if we wish to avoid bias (www.consort-statement.org).
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2 Freedman DA, Petitti DB, Robins JM. On the efficacy of screening for breast cancer. Int J Epidemiol 2004;33:4355.
3 Freedman DA, Petitti DB, Robins JM. Rejoinder. Int J Epidemiol 2004;33:6973.
4 Gøtzsche PC. Screening for breast cancer with mammography. Author's reply. Lancet 2001;358:216768.[Medline]
5 Vainio H, Bianchini F (eds). International Agency for Research on Cancer Handbooks of Cancer Prevention. Vol. 7. Breast Cancer Screening. Lyon: IARC Press, 2002.
6 Welch HG, Schwartz LM, Woloshin S. Do increased 5-year survival rates in prostate cancer indicate better outcomes? JAMA 2000;284:205355.
7 Berry DA. The Utility of Mammography for Women 40 to 50 Years of Age (Con). In: DeVita VT, Hellman S, Rosenberg SA (eds). Progress in Oncology. Sudbury: Jones and Bartlett, 2002, pp. 34672.
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