Mammography screening and risk of breast cancer death: a population-based case-control study

Because the efficacy of mammography screening had been shown in randomized controlled trials, the focus has turned on its effectiveness within the daily practice. Using individual data of women invited to screening, we conducted a case-control study to assess the effectiveness of the Dutch population-based program of mammography screening.

Cases were women who died from breast cancer between 1995 and 2003 and were closely matched to five controls on year of birth, year of first invitation, and number of invitations before case's diagnosis. ORs and 95% confidence intervals (CI) for the association between attending either of three screening examinations prior to diagnosis and the risk of breast cancer death were calculated using conditional logistic regression and corrected for self-selection bias.

We included 755 cases and 3,739 matched controls. Among the cases, 29.8% was screen-detected, 34.3% interval-detected, and 35.9% never-screened. About 29.5% of the never-screened cases had stage IV tumor compared with 5.3% of the screen-detected and 15.1% of the interval-detected cases. The OR (95% CIs), all ages (49-75 years), was 0.51 (0.40-0.66) and for the age groups 50-69, 50-75, and 70-75 years were 0.61 (0.47-0.79), 0.52 (CI 0.41-0.67), and 0.16 (0.09-0.29), respectively.

The study provides evidence for a beneficial effect of early detection by mammography screening in reducing the risk of breast cancer death among women invited to and who attended the screening.

This is the first case-control study that accurately accounts for equal screening opportunity for both cases and matched controls by number of invitations before case's diagnosis.