MUC1 and breast cancer: Targeting single antigens can lead to the risk of immune escape by the tumor, which can be reduced by targeting multiple antigens (87), for example, the bi-specific CARs HER2/IL13Ra2 (glioblastoma) and HER2/MUC1 (breast cancer) have been shown to produce superior anti-tumor responses compared to single-target therapy (87, 183).