A two-phase study is planned to validate whether functional breast imaging with a dedicated breast PET device could detect and confirm breast cancer multifocality and/or multicentricity prior to surgery. Surgeons armed with knowledge about multifocality and/or multicentricity would benefit through more rational pre-surgical planning. Existing methods of detecting multifocality and multicentricity have limited positive predictive value, or have difficulty in guiding biopsy to confirm suspected regions outside the index lesion. Phase I will lay the foundation for Phase II, by demonstrating that biopsy guidance with the device would have a sufficiently high positive predictive value in detecting cancer for an index cancer lesion to warrant proceeding to a definitive Phase II study of the device. Phase II is a prospectively-planned clinical trial testing the ability of the dedicated breast PET device to detect areas of multifocality and/or multicentricity, The gold-standard proof in this trial will be the histopathology of core biopsies of suspicious lesions (other than the index cancer) targeted using the device. The Phase II study is designed to establish that the positive predictive value for the presence of multifocality is greater than a predetermined lower-bound value (selected on the basis of prior relevant public-health determinations). Matching private funds are already committed for all phases of this SBIR project.