Screening Mammography in Finland - 1.5 Million Examinations with 97 percent Specificity

Abstract

A nationwide mammography screening program including women aged 50-59 years at the time of the first invitation and involving more than 100 radiologists was started in Finland in January, 1987. From 1987 through 1997, a total of 1690496 invitations to biennial two-view mammography screening was sent out. The compliance for screening was 88.5% with 1 495744 screening examinations performed during this 11-year period. There were 49020 recalls (3.28% of those attending) for further work-up studies and 9689 women (0.65% of those attending) were referred for surgery. The total number of screening-detected breast cancers was 5595, giving a detection rate of 3.7 cancers per 1000 screening studies. More than half (57.7%) of all surgical biopsies revealed breast cancer and 67.8% of the invasive cancers were at Stage I. The positive predictive value of referral to surgical biopsy increased from 33.2% in 1987 to 65.5% in 1997, and the ratio of malignant to benign biopsies more than tripled from the first to the fifth year of screening. The observed/expected ratio of invasive cancer detection was 2.44. Only 0.27% (1 out of every 372) of all screening mammograms were followed by a benign biopsy, and 2.90% (1 out of every 34) of all screening mammograms were followed by the women being recalled for further studies and not found to have breast cancer. This gave a specificity of recall after screening mammography greater than 97.0% and a specificity of referral to surgical biopsy greater than 99.7%. Measures of specificity improved considerably during the first three years of the screening program. The high specificity of screening mammography can be attributed to the nature of the screening process as well as to the opportunity for individual radiologists to attain a greater level of experience and competence. The decision to recall appears to have been crucial in determining the specificity. © 1999, Informa UK Ltd All rights reserved: reproduction in whole or part not permitted. All rights reserved.