Breast cancer patients participating in the Swiss mammography screening program "donna" exhibit extended survival

Study goal: We compared the survival rates of women with breast cancer (BC) within vs. outside the mammography screening program (MSP) “donna”. Methods: We merged data from the “donna” MSP with the data from corresponding cancer registries to categorize BC cases as within MSP (screen-detected and interval carcinomas) and outside the MSP. We analyzed the tumor stage distribution, tumor characteristics and the survival of the women. We further estimated hazard ratios using Cox-regressions to account for different characteristics between groups and corrected the survival rates for lead-time bias. Results: We identified 1,057 invasive (ICD-10: C50) and in-situ (D05) BC cases within the MSP and 1,501 outside the MSP between 2010 and 2019 in the Swiss cantons of St. Gallen and Grisons. BC within the MSP had a higher share of stage I carcinoma (46.5% vs. 33.0%, p<0.01), fewer metastases at diagnosis (2.7% vs. 11.6%, p<0.01), and a smaller (mean) tumor size (19.1mm vs. 24.9mm, p<0.01). The 10-year survival rates were 92.2% for women within and 73.9% for women outside the MSP (p<0.05). A significant survival difference persisted when the same tumor stages were compared. Lead-time corrected hazard ratios were 0.391 (p<0.01) for overall survival and 0.293 (p<0.01) for BC related survival. Conclusion: Women participating in the “donna” MSP had a significantly higher overall and BC related survival rate than women outside the program. Detection of BC at an earlier tumor stage only partially explains the observed differences.