Researchers will compare the breath profiles of women with breast cancer and those without to determine whether there are disease-specific patterns that can be leveraged to facilitate breast cancer detection. Women with mammogram-confirmed dense breast tissues undergoing standard-of-care breast cancer screening will be invited to participate. Those who provide informed consent will provide one breath sample and fill out a questionnaire about their medical history with help from the research coordinators. Breath samples will be collected prior to standard of care biopsy or MRI, and patients will be stratified into the case or control group based on their test results. The primary goal of this project is to use exhaled alveolar breath and the subsequent spectral data produced by Breathe BioMedical's cavity ring-down spectrometer to further develop Breathe BioMedical's technology and machine learning algorithms to determine the feasibility of detecting breast cancer in women with dense breast tissue. Secondarily, this project aims to identify patterns of VOCs that are either over- or under-represented in participants with breast cancer when compared to the breath profiles of participants without breast cancer. This project will also assess performance characteristics of the technology (e.g. sensitivity, specificity, false negative rate, and false positive rate) including subgroup analyses. This project aims to understand intra-subject variability by exploring differences in breath signatures before and after definitive management of breast cancer, including surgical resection.