BMJ  2006;332:727-728 (25 March), doi:10.1136/bmj.332.7543.727-b

Letter

Ramifications of screening for breast cancer

Definition of overdiagnosis is confusing in follow-up of Malmö trial

The first 150 words of the full text of this article appear below.

EDITOR—In their follow-up of the Malmö mammography trial, Zackrisson et al say that the reported levels of overdiagnosis vary from 5% to 50%.¹ However, to use cumulative incidence rates at the end of follow-up to quantify the level of overdiagnosis is confusing because the resulting estimates are highly sensitive to both the length of follow-up and the length of screening periods.

Suppose, for example, that during screening from age 40 to 49 the incidence is increased by 50% and that none of these extra cancers would have been detected in the patient's lifetime in the absence of screening. In this example, the level of over-diagnosis as defined by Etzioni et al would be 50% irrespectively of when follow-up is performed.² In contrast, the level of over-diagnosis as defined by Zackrisson et al would be 20% at a follow-up at age 60 but only 7% at a follow-up at . . . [Full text of this article]

Norwegian Institute of Public Health, PO Box 4404 Nydalen, N-0403, Oslo, Norway per-henrik.zahl@fhi.no

Department of Pathology, Ullevål University Hospital, N-0407 Oslo

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