Because pertuzumab and trastuzumab block HER2 in different domains, the combination of these antibodies is more effective than individual antibodies because their mechanisms of action complement each other, providing a synergistic effect10 - a stronger blockade of HER2-positive tumour cell proliferation and the ability to treat forms of cancer resistant to trastuzumab8,11. The gene discussed is ERBB2; the disease is neoplasm.