The identification of false negatives in a population of interval cancers: a method for audit of screening mammography

The Northern Region Breast Screening Radiology Audit Group (NRBSRAG) has developed a method of classifying interval cancers. Each member of the group independently reads a set of films which contains both interval cancers and controls from centres other than their own. A cancer is classified as ‘false negative’ only when it is correctly identified, on the previous screening film, by at least two members of the Group. The method avoids classifying a cancer as ‘false negative’, when the only evidence is based on retrospective searching for a trace of a tumour which is unlikely to be detected in any other way. This first analysis of 167 interval cancers shows: 46% ‘true intervals’, 26% ‘false negatives’, 11% ‘occult’, and 16% ‘not classifiable’.