Differences in Breast Cancer Characteristics by Mammography Screening Participation or Non-Participation A Retrospective Observational Study

Background: The goal of the German Mammography Screening Program (MSP) is to enable the early detection and less intensive treatment of breast cancer. We compared tumor characteristics and prognostic markers in breast cancers that were detected by screening in the MSP, in the interval after a negative screening, or among non-participants in screening. Methods: This retrospective series includes all of the 1531 cases of invasive and in situ breast cancer (DCIS, ductal carcinoma in situ) that were newly diagnosed in two certified breast care centers in Munster in the period 2006-2012 among women in the MSP target population. Complete information on the tumor characteristics, tumor biology, and primary surgical treatment were available for all cases. The mode of cancer detection was determined from the state cancer registry of North Rhine-Westphalia. Due to the retrospective design of this case series, there was no randomized allocation. Results: The 874 cases of breast cancer among MSP participants (714 detected by screening, 160 in the interval after a negative screen) and the 657 cases among non-participants arose in women of similar age (mean, 60.2 versus 59.3 years). MSP participants with breast cancer had DCIS more commonly than non-participants did (23% versus 13%); invasive carcinomas were smaller (74% versus 55% in the T1 stage), less commonly node-positive (25% versus 31%), less commonly high-grade (19% versus 27%), and less commonly triple-negative (7% versus 12%); MSP participants received neoadjuvant treatment less frequently (2% versus 8%) and more frequently underwent breast-conserving surgery (75% versus 62%). They less commonly had a guideline-based indication for adjuvant chemotherapy (46% versus 52%). Conclusion: MSP participants with invasive breast cancer can generally be treated with less intensive surgical and systemic therapy than non-participants, even if interval cancers are also taken into account. Future studies should also investigate quality of life after a diagnosis of invasive carcinoma in screening participants.