Because the average abundances (∼5,000 molecules/cell) of CARs are ∼6 and ∼600 times smaller than that of HER2 on tumor and healthy cells, respectively, most of the CARs in the CAR T cells form complexes with HER2 antigens displayed by the healthy and the tumor cells for high-affinity CARs (KD ≪ 5,000 molecules/cell). This evidence concerns the gene ERBB2 and neoplasm.