An expansion arm of a Phase I clinical trial (NCT02157792) investigating the ATR inhibitor M6620 in combination with cisplatin as a treatment for metastatic triple negative breast cancer has produced exciting initial results. In this video Melinda L. Telli, MD, from Stanford University Medical Center, Stanford, CA, speaking at the 2017 European Society for Medical Oncology (ESMO) conference held in Madrid, Spain, discusses how BRCA and P53 status were accounted for and provides an update on the progress of the study so far, including response rates and toxicity.