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

Letter

Ramifications of screening for breast cancer

1 in 4 cancers detected by mammography are pseudocancers

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

EDITOR—In this issue Zackrisson et al report on follow-up data from the Malmö mammographic screening trial and conclude that the rate of overdiagnosis of breast cancer was 10%.¹ They do not, however, calculate the risk we believe is most relevant to women considering mammography: What is the chance that a screen detected cancer represents overdiagnosis?

After 15 years of follow-up, there were 1320 diagnosed in the screened group and 1205 in the control group (table 1). The excess detection of 115 cancers associated with screening led to their conclusion of an overdiagnosis rate of 10% (115/1205).

However, because the intervention had stopped 15 years earlier and yet breast cancer cases continue to accumulate in both groups, the approach understates the risk of overdiagnosis.

A more relevant denominator is the number of cancers found in the screened group at the end of the trial—741 (table 2). This addresses the . . . [Full text of this article]

VA Outcomes Group, White River Junction, VT 05009, USA
h.gilbert.welch@dartmouth.edu

VA Outcomes Group, White River Junction, VT 05009, USA

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bmj.com, 24 Mar 2006 [Full text]

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