Beyond randomized controlled trials - Organized mammographic screening substantially reduces breast carcinoma mortality

BACKGROUND, The efficacy of mammographic screening in the reduction of brea st carcinoma mortality has been demonstrated in randomized controlled trial s. However, the evaluation of organized screening outside of research setti ngs (so-called "service screening") faces unique methodologic and conceptua l challenges. The current study describes the evaluation of organized mammo graphy screening in a clinical setting and demonstrates the benefit obtaine d from service screening in two Swedish counties. METHODS. In the group of subjects ages 20-69 years, there were 6807 women d iagnosed with breast carcinoma over a 29-year period in 2 counties in Swede n and 1863 breast carcinoma deaths. All patients were classified from patie nt charts based on their screening status (i.e., whether they had been invi ted to undergo screening and whether they actually had undergone screening) . The number of women who lived in the 2 counties during the 29-year study period was provided by the Central Bureau of Statistics. Breast carcinoma-s pecific mortality was compared across three time periods: 1) 1968-1977, whe n no screening was taking place because mammography had not been introduced ; 2) 1978-1987, the approximate period of the Two-County randomized control led trial of screening in women ages 40-74 years; and 3) 1988-1996, when al l women in the 2 counties ages 40-69 years were invited to undergo screenin g (service screening). When comparing breast carcinoma mortality in screene d women with that in women diagnosed before screening was introduced, a cor rection for self-selection bias was incorporated to prevent overestimation of the benefit of screening. RESULTS. The mortality from incident breast carcinoma diagnosed in women ag es 40-69 years who actually were screened during the service screening peri od (1988-1996) declined significantly by 63% (relative risk [RR] = 0.37; 95 % CI, 0.30-0.46) compared with breast carcinoma mortality during the time p eriod when no screening was available (1968-1977). The mortality decline wa s 50% (RR = 0.50; 95% CI, 0.41-0.60) when breast carcinoma mortality among all women who were invited to undergo screening (nonattendees included) was compared with breast cancer mortality during the time period when no scree ning was available (1968-1977). The reduction in mortality observed during the service screening period, adjusted for selection bias, was 48% (RR = 0. 52; 95% CI, 0.43-0.63). No significant change in breast carcinoma mortality was observed over the three time periods in women who did not undergo scre ening. This group included women ages 20-39 years because these individuals were never invited to undergo screening, and women ages 40-69 years who di d not undergo screening (not invited during the randomized trial or invited during the second and third time periods but declined). CONCLUSIONS. Regular mammographic screening resulted in a 63% reduction in breast carcinoma death among women who actually underwent screening. The po licy of invitation to organized screening with mammography appears to have reduced breast carcinoma mortality by 50% in these 2 counties. (C) 2001 Ame rican Cancer Society.