An Evaluation of the Prevalent round of the Breast Screening Programme in South East Thames, 1988–1993: Achievement of Quality Standards and Population Impact

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Abstract
Objective: –To evaluate the impact of the prevalent round of the NHS breast screening programme on the whole population of women aged 50–64 during the period 1988–92, by comparing the numbers of cancers detected at screening with those diagnosed symptomatically, in one United Kingdom health region (population 3.5 million). To relate this impact to the achievement of national quality standards and the observed sensitivity and specificity of the programme. Method: –The breast screening programme computer systems and the Thames Cancer Registry database were used to diagnose cancers in women aged 50–64 during the period 1988–1992, who were classified into screen detected, interval cases, eligible but not yet invited, non-attenders, and those not registered with the programme. Results: –The programme met all national quality assurance targets for uptake, diagnostic process, and detection, but screen detected cases comprised only 48% of those diagnosed during 1991 and 1992 when the breast screening programme was fully operational. As fewer than 40% of breast cancers registered occur in the eligible age range, this limits the impact of the programme to the possible early diagnosis of only 20% of all cases. A surprisingly high proportion occurred in women unknown to the programme, especially in inner London. The high number of interval cancers led to a programme sensitivity of only 73%, but 99.7% of women screening negative were correctly reassured as a result of screening—and for them the breast screening programme is a success. Conclusion: –Despite achievement of quality standards, the breast screening programme is apparently having a low impact on the overall diagnosis of breast cancer in South East Thames, so a large mortality reduction due to screening alone is unlikely. Population coverage will need to be improved, and it may be necessary to reduce the screening interval, or extend the age range, or both.