Cross‐reacting material 197 (CRM197), an HB‐EGF inhibitor, is a nontoxic mutant of diphtheria toxin, which shares immunological properties with the native molecule.5, 6 CRM197 binds to the soluble form of HB‐EGF as well as pro‐HB‐EGF and blocks mitogenic activity by inhibiting the binding between EGFR and HB‐EGF.7 Although CRM197 does not inhibit the mitogenic activity of other EGFR ligands, it is a specific inhibitor of HB‐EGF and the only known inhibitor that can be used for cancer therapy in mice and humans.8 The gene discussed is HBEGF; the disease is cancer.