Thirty years of population-based breast cancer screening in Iceland: a comparison of quality indicators and tumour characteristics between women aged 40-49 and 50-69 years.

Background and purpose: Organised mammography screening reduces breast cancer mortality by 30-40% in women aged 50-69. Despite limited evidence for women aged 40-49, screening guidelines are trending toward younger ages. Iceland has offered biennial screening to women aged 40-69 since 1987. This study compares screening quality indicators and tumour characteristics between women aged 40-49 and 50-69 from 1990 to 2020. Patient/material and methods: Screening-related data were obtained from the Icelandic Breast Cancer Screening Program, and breast cancer diagnoses and tumour characteristics were sourced from the Icelandic Cancer Registry.

Results: In total, 84,677 women aged 40-69 years attended 455,532 organised screening sessions in Iceland over a 30-year period. Women aged 40-49 years demonstrated higher recall rates (4.9% vs. 3.5%) and lower participation rates (60.7% vs. 61.5%), lower breast cancer detection rates (2.1 vs. 6.0/1,000), and lower episode sensitivity (54.8% vs. 70.5%), compared to those aged 50-69 years. Among screen-detected cases, women aged 40-49 years exhibited a higher proportion of tumours larger than 20 mm (29.7% vs. 21.7%), more lymph node positivity (41.2% vs. 28.2%) and higher human epidermal growth factor receptor 2 (HER2) positivity (18.6% vs. 11.8%), compared to those aged 50-69 years.

Interpretation: The disparity in breast cancer screening performances between the age groups may reflect unmodifiable factors in younger women. The presence of advanced tumour characteristics among women aged 40-49 years who attended screening indicates the importance of early detection for improving prognosis.