Utomilumab, a 4-1BB receptor IgG2 mAb agonist, is currently being developed in combination with trastuzumab or T-DM1 for the treatment of patients with advanced HER2+ breast cancer in a phase 1 dose-escalation trial (NCT03364348) and in combination with avelumab in a phase 2 trial (AVIATOR, NCT03414658) (Table 1). This evidence concerns the gene ERBB2 and breast cancer.