Project Summary/Abstract (Administrative Core Component, RFA-CA-22-040) We propose to develop a blood-based test whose indicated use is to complement mammography in the early detection of breast cancers. Although mammography saves lives through early detection, it is imperfect. Approximately one in seven breast cancers goes undetected despite screening mammography, and interval cancers that manifest within a year of a normal mammogram remain a vexing problem, especially (although not exclusively) for the >27 million women in the United States with heterogeneously or extremely dense breasts at high risk for interval cancers. We propose to develop a blood test that could be used as an adjunct to mammography to improve early detection by improving sensitivity and/or specificity of mammography. Using a novel biomarker discovery approach leveraging human-in-mouse breast cancer patient-derived xenograft models and state-of-the-art mass spectrometry methods, we prioritized a subset of 162 candidate breast cancer protein biomarkers (verified in human plasma from breast cancer cases vs. controls) for follow up EDRN phase 2 validation studies in this proposed BCC. Our project will clinically validate and deploy (in our CLIA laboratories) a novel multiplex immuno-multiple reaction monitoring mass spectrometry (immuno-MRM-MS) assay to perform EDRN phase 2 biomarker validation studies using strongly unbiased sets of plasma samples obtained from existing biorepositories. The Administrative Core will support all aspects of the BCC, including managing all administrative and project management aspects of the BCC (e.g., budgets, contracts, timelines, IRB documentation, site visits, travel arrangements, progress reports, manuscript submission), as well as managing all center logistics and communication (e.g., coordination of all communications within the BCC, between the BCC and NCI, and between our BCC and others in the Network).