However, this approach is likely to come with significant safety concerns, noting particularly the famous case of a HER2-specific CAR T cell causing respiratory failure and death in a patient lung- and liver-metastatic HER2+ breast carcinoma, revealing a potential ‘on-target, off-tumour’ effect of CAR T cells directed at a target also found in normal tissue [69]. This evidence concerns the gene ERBB2 and breast carcinoma.