Positron emission mammography (PEM) provides images of biochemical activity in the breast with spatial resolution matching individual ducts (1.5 mm full-width at half-maximum). This spatial resolution, supported by count efficiency that results in high signal-to-noise ratio, allows confident visualization of intraductal as well as invasive breast cancers. Clinical trials with a full-breast PEM device have shown high clinical accuracy in characterizing lesions identified as suspicious on the basis of conventional imaging or physical examination (sensitivity 93%, specificity 83%, area under the ROC curve of 0.93), with high sensitivity preserved (91%) for intraductal cancers. Increased sensitivity did not come at a cost of reduced specificity. Considering that intraductal cancer represents more than 30% of reported cancers, and is the form of cancer with the highest probability of achieving surgical cure, it is likely that the use of PEM will complement anatomic imaging modalities in the areas of surgical planning, high-risk monitoring, and minimally invasive therapy. The quantitative nature of PET promises to assist researchers interested studying the response of putative cancer precursors (e.g., atypical ductal hyperplasia) to candidate prevention agents.