Is the three year breast screening interval too long? Occurrence of interval cancers in NHS breast screening programme's north western region

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Abstract
Objective: To report the detection rate of interval cancers in women screened by the NHS breast screening programme. Design: Detection of interval cancers by computer linkage of records held by the screening centres in the North Western Regional Health Authority with breast cancer registrations at the regional cancer registry. Setting: North Western Regional Health Authority. Subjects: 137421 women screened between 1 March 1988 and 31 March 1992 who had a negative screening result. Results: 297 invasive interval cancers were detected. The rate of detection of interval cancers expressed as a proportion of the underlying incidence was 31% in the first 12 months after screening, 52% between 12 and 24 months, and 82% between 24 and 36 months. Conclusion: The incidence of interval cancers in the third year after breast screening approaches that which would have been expected in the absence of screening and suggests that the three year interval between screens is too long. Key messages The NHS breast screening programme invites all women aged 50–64 to be screened every three years To be successful, the incidence of cancers presenting with symptoms between screening appointments—that is, interval cancers—must be kept low More interval cancers than predicted are occurring, and after 24 months the incidence approaches that expected in the absence of screening To reduce the incidence of interval cancers it may be necessary to shorten the screening interval