We are tempted to speculate that because pertuzumab and trastuzumab are known to recognise two different HER2/neu epitopes, the combined use of both antibodies may have caused a net increase in antibody binding to the surface of HER2/neu-positive tumour cells and, consequently, an increased tumour susceptibility to trastuzumab and pertuzumab-mediated ADCC. This evidence concerns the gene ERBB2 and neoplasm.