CD274 and breast cancer: The combination of ICIs with traditional HER2 inhibitors such as trastuzumab has poor efficacy, while ICIs combined with HER2-targeted antibody-drug conjugates (ADCs), such as trastuzumab emtansine or the novel ADC T-DXd, showed an effective response in HER2-positive PD-L1 positive breast cancer or metastatic HER2-positive gastric or gastro-esophageal junction adenocarcinoma, which still needs to be further confirmed.