CD274 and breast cancer: The KATE2 trial, which tested the addition of the anti-PD-L1 antibody atezolizumab to trastuzumab emtansine in metastatic BC HER2+ BC patients previously treated with trastuzumab and taxanes, despite missing its primary endpoint, identified a numerically longer PFS and higher 1-year OS in patients with PD-L1+ and TIL high (≥5%) tumours20.