This conference will focus on rare cells in circulation with a focus on human disease. Epithelial progenitor and stem cells, mesenchymal cells, fetal cells, and circulating tumor cells are normally relegated to extravascular organs but can traffic within the blood stream to initiate a number of important biological processes, such as organ repair and regeneration, angiogenesis, and metastasis. Thus, these cells represent a critically important population within the circulation and can provide a unique view into organ status, fetal health, and disease evolution. However, given their rarity within the circulation, the study of these cells poses unique challenges that will require innovative multi-disciplinary approaches. To catalyze this embryonic field, we will bring together engineers, biologists, and clinicians to address the wide range of interest in these rare cell populations. The first conference will focus on cancer-relevant cells, primarily circulating tumor cells, including capture technology, definition of the population, correlation with disease diagnosis and progression, functional and molecular characterization, and relation to therapy.