The value of the second view in screening mammography

Abstract

A prospective study of 33,734 women was undertaken during the prevalent round of the UK National Breast Screening Programme. The cancer detection rates and recall rates were compared between a one view and a two view technique. In one fifth of the women, only the single oblique view examination was read. To lose the bias that would have been introduced by the prior knowledge that a second view would be available, the radiologists reading the oblique view did not know whether or not a craniocaudal view would subsequently be available. Readings were available from two radiologists in each case. The cancer detection rate increased from 7.6 per thousand to 8.2 per thousand women screened, with 14 more cancers detected with the two view technique. This represents 6.5% of all screen detected cancers (95% CI 3.2-9.8). The recall rate was reduced from 8.8% to 6.6% by the second view (p < 0.001). There was a significantly higher biopsy rate in the two view group (10.6/1000 versus 8.6/1000) (p = 0.004). This higher biopsy rate is part of the price paid for the higher detection rate. The additional tumours included small invasive cancers. The National Health Service (NHS) cost of each additional cancer diagnosed was 4129 pounds and the NHS plus private cost was 2742 pounds. These findings have practical applications for the National Breast Screening Programme. There would be resource implications on routinely applying two view screening to the prevalent round, but even greater costs if applied to the incident screening round.