Effectiveness of screening a small population

Guernsey provides healthcare for a population of 60,000. An on-island breast screening programme has existed since March 1995, with a 2-year screening round. Data have been analysed for six screening rounds to the end of March 2007, and have been evaluated against the National Health Service Breast Screening Programme (NHSBSP) Pritchard Standards. The small cohort size (<4,000 per annum) necessitates off-island screen reading by NHSBSP readers. Assessments are performed in Guernsey by a single breast radiologist. The majority of breast surgery is performed in Guernsey. Over the six screening rounds, a total of 39,166 screening mammograms have been performed, 2,542 assessment visits have been made, and 208 cancers have been identified (149 invasive, 59 ductal carcinoma in situ). Examples of standards evaluated for the six rounds: compliance, >90%; standardised detection rate, range 0.6 to 1.83; small cancer detection rates, 2.46/10,000 (average); interval cancers, 1.22 per 1,000 screened (average); 10-year survival from screen-detected cancers, 92%. These data show an effective screening programme assessed by Pritchard Standards, and demonstrate a model for the delivery of breast screening in a small isolated population.