The Scottish breast screening programme's experience of monitoring interval cancers

Objectives-To present the Scottish interval cancer data fi om 1991 to 1995, compare the Scottish experience with results published by other programmes and trials, and document appropriate methodologies to achieve maximum ascertainment of interval cancers.

Setting-Scottish breast screening programme (part of the UK National Health Service breast screening programme).

Methods-Interval cancers were identified by linking breast screening data with registrations of invasive breast cancers from the National Scottish Cancer Register. The main outcome measures were the numbers, rates, and proportionate incidence of interval cancers, and rates of total and small (<10 mm) screen detected invasive cancers diagnosed in this cohort of women.

Subjects-Women who attended the Scottish breast screening programme (Scottish NHSBSP) from 1 April 1991 to 31 March 1995.

Results-Interval cancer rates of 4.8, 12.1, and 12.1 per 10 000 women screened were calculated for the first, second, and third year after the last negative screen. Expressed as a proportion of the underlying incidence, the figures are 23%, 60%, and 59%.

Conclusions-The Scottish data are comparable with those reported by other UK NHS breast screening programmes for the first and second years after the last negative screen. The interval cancer rate for the third year is appreciably lower. A longer follow up period would be of interest to provide greater evidence on which to base comparisons. Ascertainment of interval cancers depends vitally on the availability of complete, accurate, and timely national cancer registration data and highlights the value of national datasets.