The treatment of HER2-positive cancers has changed significantly over the past ten years thanks to a significant number of promising new approaches that have been added to our arsenal in the fight against cancer, including monoclonal antibodies, inhibitors of tyrosine kinase, antibody–drug conjugates, vaccination, and particularly, adoptive-T-cell therapy after its great success in hematological malignancies. This evidence concerns the gene ERBB2 and cancer.