BMJ 1995;310:1002 (15 April)

Letters

Incidence of interval cancer and detection rate of first screenings are inconsistent

EDITOR,--Ciaron B J Woodman and colleagues report the first data on interval cancers from the NHS breast screening programme.1 They do not comment on a serious inconsistency between the incidence of interval cancers and the detection rate at first screening, which deserves attention before conclusions are drawn from the data.

The incidences in the first three years after screening are 31%, 52%, and 82% of the underlying incidence. This reduction in incidence after screening occurs because of the cancers that were detected by screening. In these three years the reduction is (3x100%)-31%-52%-82%=135% of the yearly incidence. The steep increase in the incidence of interval cancer back to the underlying incidence suggests that the cumulative reduction in incidence will not be much higher than 135% in following years.

The reported detection rate at first screening is 5.9/1000 screens. Thus the number of cancers detected at first screening is 322% of the . . . [Full text of this article]


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Relevant Article

Is the three year breast screening interval too long? Occurrence of interval cancers in NHS breast screening programme's north western region
Ciaran B J Woodman, Anthony G Threlfall, Caroline R M Boggis, and Pat Prior
BMJ 1995 310: 224-226. [Abstract] [Full Text]

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