The ongoing phase 3 KATE3/MP42319 (NCT04740918) trial is randomizing patients with HER2+ and PD-L1+ advanced breast cancer to T-DM1, with or without atezolizumab in the second-line setting, while NCT03199885 is assessing the role of atezolizumab in combination with a taxane, trastuzumab and pertuzumab in the first-line setting in a PD-L1 unselected patient population. This evidence concerns the gene CD274 and breast carcinoma.