Maria Papadaki, PhD, University of Crete, Heraklion, Greece, gives an overview of a study of the correlation between circulating tumor cells (CTCs) bearing cancer stem cells (CSCs), epithelial-to-mesenchymal (EMT) phenotypes and immunosuppressive cell types in the peripheral blood of patients with metastatic breast cancer. This interview took place at the virtual European Society for Medical Oncology (ESMO) Breast Cancer Congress 2021.