The goal of this observational study is to evaluate the feasibility and effectiveness of using non-contrast chest computed tomography scans for opportunistic breast cancer screening, and to further compare its diagnostic performance with conventional imaging modalities, including mammography and/or breast magnetic resonance imaging.

Breast cancer is one of the most common malignancies in women, and early detection is essential for improving clinical outcomes. While dedicated breast imaging modalities, including mammography and breast MRI, are widely used for screening. Many women undergo non-contrast chest CT scans for other clinical indications, providing a potential opportunity for breast evaluation. This observational study aims to investigate the clinical value of non-contrast chest CT scans as an opportunistic screening tool for breast cancer. Breast tissue visible on routine CT scans will be assessed using artificial intelligence-based methods to identify suspicious lesions. The primary objective is to evaluate the diagnostic performance of non-contrast chest CT in detecting breast cancer, including sensitivity, specificity, and accuracy, and to further compare its diagnostic performance with mammography and breast MRI. The findings are expected to determine whether non-contrast chest CT can serve as an opportunistic tool for early breast cancer detection without additional imaging burden, and to clarify its relative clinical value compared with established breast imaging techniques.

Inclusion Criteria:

1. Female patients who have undergone non-contrast chest CT examination;
2. Participants included in the comparative analysis must have undergone at least one comparator imaging modality (mammography and/or breast MRI);
3. If a breast lesion is detected, it must be confirmed by pathology or clinical follow-up at least 12 months;
4. No prior systemic or local therapy before imaging examinations;
5. Imaging data are complete and of sufficient quality for analysis.

Exclusion Criteria:

1. History of other malignancies with potential impact on breast imaging interpretation;
2. Participants with suspected malignant breast lesions but no confirmation;
3. Prior radiotherapy, chemotherapy, or immunotherapy before imaging examinations;
4. Imaging data that are incomplete, of poor quality, or contain significant artifacts preventing reliable analysis;
5. Time interval between non-contrast chest CT and comparator imaging modalities exceeding three months, or with clinical events occurring between examinations that may alter lesion status.

The study population consists of female patients undergoing non-contrast chest CT scans for any clinical indication at participating institutions, with or without breast lesions detected on CT. For participants included in the comparative analysis, at least one additional breast imaging modality (mammography and/or breast MRI) must have been performed within three months of the non-contrast chest CT examination and without any intervening clinical events.