Most therapeutic targets are tumor-associated antigens (TAAs), that are expressed at low levels on healthy cells (i.e. epidermal growth factor receptor (EGFR) [3], human epidermal growth factor receptor 2 (HER2) [4], mucin 1 (MUC1) [5] and carcinoembryonic antigen (CEA) [6]) leading to on-target off-tumor (OTOT) toxicity due to CAR-T cell targeting of those low TAA expressing cells. The gene discussed is CEACAM5; the disease is neoplasm.