NEW SWEDISH BREAST-CANCER DETECTION RESULTS FOR WOMEN AGED 40-49

The issue of whether to screen women aged 40-49 for breast cancer is d ebated usually in terms of the potential mortality reduction achievabl e by the application of screening in this age group. Theories regardin g why a significant reduction in mortality has not been observed in tr ials relate to the biologic behavior of tumors in this age group and t he screening process itself. Survival curves with respect to node stat us, size, and grade of the tumor were compared among age groups in the Swedish two-county trial. In the Kopparberg part of this trial, for t he 40-49 age group, predicted survival was calculated from the size, n ode status, and grade of cancers detected during the trial in comparis on with those found in two later series of tumors, one from the 1989-1 992 Kopparberg screening program, the other from the British Columbia screening program that began in 1988. The Kopparberg arm of the Swedis h two-county study used single-view mammography with extended processi ng but without grid; the two more recent programs used two-view mammog raphy with extended processing and the grid. Both the Kopparberg progr ams used a 2-year interval. The effects of grade, node status, and siz e on survival in the 40-49 age group were very similar to their effect s in older age groups. Predicted survival from the later Kopparberg se ries was essentially the same as that for the earlier. The mortality r eduction in this age group in the Kopparberg part of the Swedish two-c ounty trial was 26%. The survival results indicate no biologic reason why screening should not be able, theoretically, to reduce mortality. Nonsignificant reductions in mortality have been observed in the Koppa rberg part of the two-county trial and in the overview of Swedish tria ls. The similar predictive results for the two-view and one-view trial s suggest that the most likely way to achieve further reductions in mo rtality is to reduce the interval between screens, possibly to 1 year.