Effectiveness of Organized Mammography Screening for Different Breast Cancer Molecular Subtypes.

Background: Screening program effectiveness is generally evaluated for breast cancer (BC) as one disease and without considering the regularity of participation, while this might have an impact on detection rate.
Objectives: To evaluate the short-term effectiveness of a mammography screening program for the major molecular subtypes of invasive BC.
Methods: All women who participated in the screening program and were diagnosed with screen-detected or interval BC in Flanders were included in the study (2008-2018). Molecular subtypes considered were luminal and luminal-HER2-positive, human epidermal growth factor receptor 2-positive, and triple-negative BC (TNBC). The relationship between the BC stage at diagnosis (early (I-II) versus advanced (III-IV)) and the method of detection (screen-detected or interval) and the relationship between the method of detection and participation regularity (regular versus irregular) were evaluated by multi-variable logistic regression models. All models were performed for each molecular subtype and adjusted for age.
Results: Among the 12,318 included women, BC of luminal and luminal-HER2-positive subtypes accounted for 70.9% and 11.3%, respectively. Screen-detected BC was more likely to be diagnosed at early stages than interval BC with varied effect sizes for luminal, luminal-HER2-positive, and TNBC with OR:2.82 (95% CI: 2.45-3.25), OR:2.39 (95% CI: 1.77-3.24), and OR:2.29 (95% CI: 1.34-4.05), respectively. Regular participation was related to a higher likelihood of screening detection than irregular participation for luminal, luminal-HER2-positive, and TNBC with OR:1.21 (95% CI: 1.09-1.34), OR: 1.79 (95% CI: 1.38-2.33), and OR: 1.62 (95% CI: 1.10-2.41), respectively.
Conclusions: Regular screening as compared to irregular screening is effective for all breast cancers except for the HER2 subtype.