Age-Specific Effectiveness of the Nijmegen Population-Based Breast Cancer-Screening Program: Assessment of Early Indicators of Screening Effectiveness

Abstract

The benefits of mammographic screening for breast cancer are not clear for women less than 50 years old. Our aim was to evaluate the effectiveness of breast cancer screening in different age groups. A mammographic breast cancer-screening program with a 2-year screening interval has been under way in Nijmegen, The Netherlands, since 1975. After eight rounds, more than 40,000 women have been invited to participate. All breast cancer cases diagnosed in the invited population, whether detected by screening or clinically, have been considered in this study. The age groups are younger than 50 years, 50-69 years, and 70 years or older at last invitation before diagnosis. Our assessment of the effectiveness of screening is based on the proportion of screen-detected cancers among all cancers and on the disease stage at diagnosis. For women younger than 50, compliance was 75%, and 37% (85/230) of the cancers were detected by screening. The age group 50-69 years had a compliance of 65% with 48% (288/595) of cancers detected by screening, and the group 70 years or older had a 25% compliance with 35% (108/305) of cancers detected by screening. The sizes of the cancers detected by screening were smaller than those detected clinically for all age groups. The age group under 50 showed no substantial difference in the proportion of positive axillary lymph node status between screening-detected and clinically diagnosed cancers, while among older women, the proportion of lymph node involvement was substantially higher for clinically detected cases. A significantly lower frequency of advanced stages was observed in screen-detected compared with clinically diagnosed cancers for women 50 years of age or older (P < .001) but not in women under 50 (P = .35). No positive effect of the biennial screening program is apparent for women under age 50. For women aged 50 and above, the screen-detected cancers have a more favorable stage distribution than clinically diagnosed cancers, a prerequisite for a reduction in breast cancer mortality.