Breast cancer screening programmes in Switzerland, 2019-2021

This sixth national monitoring report mandated by Swiss Cancer Screening presents the results of organized mammography screening for the years 2010-2021 with focus on 2019-2021. The report covers all 10 regional programmes in 14 cantons. The analyses are based on more than 3 million anonymized records. This report mainly focuses on the outcomes of screening in women aged 50-69. Results for first-time attending women aged 50-51 and women aged 70-74 in programmes that systematically invite this older age group are also presented.

In 2023, 60% of women in Switzerland aged 50-69 and 44% of those aged 70-74 were covered by organized mammography screening. The increase in geographical coverage by public programmes is slow and population coverage remains comparatively low for a European country. Participation has steadily increased over time since the beginning of monitoring (2010-2012) and reached 47% for general participation and 41% for first-round participation in 2019-2021. It varied little across age groups. The range in general participation between programmes (36-60%) slightly narrowed over time. Reattendance rate remained around 82%. The COVID-19 pandemic likely had only a punctual impact on screening activity and participation.

Quality of screening differed largely between first and subsequent screening. In 2019-2021, the referral rate for prevalent (first) screening exceeded the acceptable level of the European Guidelines (98.5 vs 70 per 1000 screens recommended) whereas the acceptable standard was largely met for incident (subsequent) screening (31 vs 50 per 1000). Prevalent referral rates varied nearly three-fold across programmes with only one programme (BE) satisfying the recommended threshold. This upward trend corroborated results from the previous national monitoring and from longstanding programmes in Europe. Consequently, risk of false-positive results was high, and the positive predictive value (PPV) of mammography screening further decreased to 7.4%. In contrast, performance in incident screening was satisfying, more homogenous across programmes and stable over time. The PPV was 16.2%, more than twice that observed for prevalent screens. This value was particularly high in women aged 70-74 (25.9%) due to their higher breast cancer risk and detection rate (8.9 per 1000 screens). Out of 1000 first-time screened women, 90 experienced a false-positive result (31 in subsequent screens) and 19 an invasive investigation without a cancer diagnosis (4 in subsequent screens). Screening-related risks were highest for first-time participants aged under 52 and lowest for women aged 70-74 years. The increasing discrepancy in quality indicators for prevalent and subsequent screening, performed by the same pool of radiologists in the programmes, warrants further investigation into the medical approach for younger, first-time screened women.

The profile of screen-detected cancers was stable over time and globally met the recommended levels. If, as expected, prognostic profile was more favourable for cancers detected in incident than in prevalent rounds, this difference reduced over time.