CT-AI Breast Cancer Opportunistic Screening Health Examination Study

Inclusion Criteria: * Female participants aged 18 to 80 years. * Undergoing routine health examination. * For the prospective phase, no clear ongoing breast-related symptoms at baseline. * Availability of complete non-contrast chest CT images. In the prospective phase, chest CT must have been scheduled as part of the routine health examination or for another established clinical purpose and must not be performed solely for this study. * Availability of a contemporaneous routine breast ultrasound report and relevant clinical information. * Chest CT image quality adequate for AI analysis. * Availability of an appropriate follow-up pathway through hospital records, pathology systems, cancer registry data, or approved follow-up methods. * For the prospective phase, study information has been provided through an ethics-approved process and the participant has not actively opted out. Exclusion Criteria: * Previous diagnosis of breast cancer, prior treatment for breast malignancy, or breast malignancy already confirmed before baseline. * Pregnancy or breastfeeding. * Incomplete breast coverage on chest CT, severe image artifacts, missing images, or other conditions that prevent valid AI analysis. * Critical baseline or outcome data are substantially incomplete and cannot reasonably be recovered. * No effective follow-up pathway can be established. * For the prospective phase, the participant actively opts out before AI analysis or explicitly declines use of imaging and clinical data for this study.