Two-view mammography: the Welsh experience and overview

Abstract

In Wales, population breast screening using mammography, within the National Health Service Breast Screening Programme (NHSBSP), commenced in February 1989. It was gradually rolled out across the Principality over the next 3 years by Breast Test Wales with the prevalent screening round completing in 1995. From its inception, two-view mammography was the standard for all prevalent round screens in Wales, unlike many other screening programmes that relied on a single view. This resulted in higher than expected cancer detection rates as compared with the Swedish Two County trial and other NHSBSP results. In Wales 9.2 breast cancers per 1000 women screened were found compared with an average of 6.3 per 1000 in the rest of the UK in the prevalent round. For incident round screens, it was decided that single-view mammography was appropriate. The results were less impressive, with cancer detection dropping to standardised detection ratio values of less than one. There may be several reasons for this anomaly, not least of which is the possibility that more subtle cancers, including those only visible on the cranio-caudal view, had been identified at the prevalent screen and were thus not present to be picked up at subsequent incident rounds. In 2000, when the National Assembly for Wales made monies available to extend screening up to the age of 70 years, it was decided that, firstly, the programme should revert to two-view screening, but this time for all rounds. The results of these first two-view incident round figures will be presented. There has been an increase in cancer detection of around 39%, similar to that predicted by Blanks and Moss in their studies. The first 18 months of two-view incident round screening increased the cancer detection rate in these women from 5.38 to 7.5 per 1000 screened. This included an increase in the small cancers detected from 2.30 to 3.30 per 1000. The recall to assessment figures also rose, surprisingly from 3.8% to 4.5%, although the rise has not been sustained more recently. In some areas the first incident two-view round has been completed; data on this will be presented. It is, however, unlikely that this increase in cancer detection will persist in subsequent incident rounds and a steady state will be reached, but at a higher level of cancer detection than with single-view incident screening. It is hoped that, in contrast, the interval cancer rate will drop accordingly. Early data on interval cancers will also be presented.