ERBB2 and breast cancer: HER2CLIMB-04 is a phase II clinical trial designed to investigate the efficacy and safety of combining these two molecular targeted-HER2 therapies in patients with HER2+ breast cancer who have undergone previous treatments, including taxane and trastuzumab, with or without pertuzumab or have experienced disease progression within 6 months after neoadjuvant or adjuvant treatment with taxane and trastuzumab, with or without pertuzumab.