CD274 and breast cancer: Moreover, another phase Ib/II study (PANACEA (IBCSG 45 − 13/BIG 4–13/KEYNOTE-014)) analyzed the synergistic effect of pembrolizumab and trastuzumab in patients with trastuzumab-resistant HER2-positive breast cancer; although PD-L1 positive patients initially responded, they ultimately developed resistant disease [34].