T-cell receptor, or TCR, therapy is a cancer treatment that genetically reprograms immune cells, called T cells, to hunt down cancer with precision. It’s similar to another treatment, CAR T-cell therapy, but with one key difference: CAR T-cell therapy can only spot proteins that naturally appear outside a cancer cell. TCR therapy, however, can also catch small protein fragments from inside the cell that are carried to the surface and displayed like little name tags.