MUC1 and esophageal squamous cell carcinoma: CAR T cells targeting putative solid tumor antigens, including Ganglioside G2 (GD2), mesothelin, B-cell maturation antige (BCMA), prostate-specific membrane antigen (PSMA), Epidermal Growth Factor Receptor Variant III (EGFRvIII), Mucin 1 (MUC1), and New York Esophageal Squamous Cell Carcinoma-1 (NY-ESO-1), are all under active investigation.4