ERBB2 and breast cancer: Priceman et al.93 have optimized HER2-CAR T cells containing either CD28 or 4-1BB intracellular costimulatory signaling domains and have demonstrated robust antitumor efficacy after the regional intraventricular delivery of HER2-CAR T cells for the treatment of HER2+ breast cancer metastasis to the brain in a mouse model.