MUC1 and breast cancer: Breast cancer targeting using CAR technology has been well documented with studies reporting the generation of CAR for breast cancer-associated tumour antigens such as carbonic anhydrase IX [22], ERBB2 [23], mesothelin [24], EGFR variant III (EGFRvIII) [25], carcinoembryonic antigen (CEA) [26], and Mucin-1 (MUC-1) [27].