EFFICIENCY OF CANCER-DETECTION DURING ROUTINE REPEAT (INCIDENT) MAMMOGRAPHIC SCREENING - 2-VIEW VERSUS ONE-VIEW MAMMOGRAPHY

Objective-To examine the influence of one view versus two view mammogr aphy on cancer detection and recall for further investigation of women attending incident (subsequent) screening. Setting-All cancers (invas ive and in situ) detected as incident cases during the second screenin g round (January 1994 to January 1997) at the South West London Breast Screening Service were used. This service uses two view mammography a nd double reading, with arbitration by a third or further readers for all screens. Methods-Mammograms of cases were mixed with those of cont rols in a 1:2 ratio in nine test sets; each set was read Independently by three film readers. Fourteen readers, each reading from one to fou r test sets, took part in the study. Initially, the oblique view only was read, then the craniocaudal view was read in addition. Previous fi lms were available to the readers. Data on abnormalities noted on the films and probability of recall were recorded and analysed. Results-10 of the 14 readers obtained increased sensitivity using two views (p=0 .04), for two readers there was no difference, and for two readers sen sitivity decreased. The mean sensitivity increase was 6.1% (p=0.01). T he overall increase in sensitivity from all readings of invasive cance rs was 8.9%, with no increase seen for in situ cancers. 11 of the 14 r eaders obtained an increase in specificity (p=0.006), two readers show ed no increase, and the specificity for one reader was decreased. The mean increase in specificity using two views was 5.7% (p=0.006). Concl usion-This study showed an increase of 8.9% in sensitivity for the det ection of invasive cancers when two views are used at incident screeni ng, with a ratio of two control mammograms for every case. This is equ ivalent to a sample from population screening with a cancer detection rate of 333 per 1000. Such a study is considered to be likely to under estimate the benefit of two views in screening under non-test conditio ns where the cancer detection rate is of the order of five per 1000. T he use of two view mammography for the detection of in situ cancers sh owed no increased benefit. A randomised controlled trial is needed to obtain a reliable estimate of the increase in cancer detection rate fo r incident screening in normal populations.