ERBB2 and cancer: We next tested the capacity of ebselen oxide to inhibit the activation of several mutated and truncated forms of HER2 associated with resistance to anti‐HER2 therapeutic agents, including the truncated form of HER2 (p95HER2), which is expressed in up to 30% of HER2+ tumors and presents intrinsic resistance to antibody‐based therapies [4, 5, 19] and V777L HER2 and V842I HER2, two activating somatic mutations of HER2 kinase domain found in 4.0% and 4.4% of all cancers, respectively, and associated with trastuzumab and/or resistance to kinase inhibitors [24, 25].