We then investigated the effect of ebselen oxide on other HER2+ cancers cells using gastric (NCI‐N87) and ovarian (SKOV3) cell lines, which display high expression levels of HER2 and exhibit strong HER2‐dependent proliferation as revealed by the decrease of both HER2 activation and proliferation capacity with AG1478, a nonspecific kinase inhibitor of HER2 (Fig. S4). The gene discussed is ERBB2; the disease is cancer.