Evanthia T. Roussos Torres, MD, PhD, Keck School of Medicine of USC, Los Angeles, CA, discusses the preclinical research looking into the mechanisms of action of entinostat on different cell populations within breast cancer tumors. Through biomarker analysis, Dr Torres hopes to understand the changes in T cells, myeloid-derived suppressor cells, and macrophages in patients with metastatic breast cancer. This interview took place at the European Society for Medical Oncology (ESMO) 2021 congress.