ERBB2 and breast cancer: Not only does it competitively occupy the ATP-binding site on EGFR, but it also binds to the unique amino acid residue Cys805 near the opening of the pocket-a homologous cysteine residue to EGFR Cys797-to undergo alkylation or covalent bonding, thus achieving irreversible inhibition of HER2.154,155 Neratinib was approved by the FDA in July 2017 for the treatment of breast cancer, making it the only product in the world approved for intensive adjuvant therapy with trastuzumab (herceptin) in HER2-positive breast cancer to reduce the risk of recurrence.