Patient-reported outcomes and hospitalization data in patients with HER2-positive metastatic breast cancer receiving trastuzumab deruxtecan or trastuzumab emtansine in the phase III DESTINY-Breast03 study.

BACKGROUND: In the DESTINY-Breast03 clinical trial, trastuzumab deruxtecan (T-DXd) showed superior progression-free survival and overall survival versus trastuzumab emtansine (T-DM1) and manageable safety in patients with human epidermal growth factor receptor 2 (HER2)-positive (HER2+) metastatic breast cancer. Here, patient-reported outcomes (PROs) are reported along with hospitalization data. PATIENTS AND METHODS: Patients in DESTINY-Breast03 were assessed for prespecified PRO measures, including European Organization for Research and Treatment of Cancer quality of life (EORTC-QoL) questionnaires [the oncology-specific EORTC Quality of Life Questionnaire Core 30 (QLQ-C30) and breast cancer-specific EORTC QLQ-BR45] and the generic EuroQol 5-dimension 5-level questionnaire (EQ-5D-5L) visual analogue scale. Analyses included change from baseline, time to definitive deterioration (TDD), and hospitalization-related endpoints. RESULTS: EORTC QLQ-C30 baseline global health status (GHS) scores for T-DXd (n = 253) and T-DM1 (n = 260) were similar, with no clinically meaningful change (<10-point change from baseline) while on either treatment (median treatment duration: T-DXd, 14.3 months; T-DM1, 6.9 months). TDD analyses of QLQ-C30 GHS (primary PRO variable) and all other prespecified PROs (QLQ-C30 subscales, the QLQ-BR45 arm symptoms scale, and the EQ-5D-5L visual analogue scale) suggested T-DXd was numerically favored over T-DM1 based on TDD hazard ratios. Of all randomized patients, 18 (6.9%) receiving T-DXd versus 19 (7.2%) receiving T-DM1 were hospitalized, and the median time to first hospitalization was 219.5 versus 60.0 days, respectively. CONCLUSIONS: In DESTINY-Breast03, EORTC GHS/QoL was maintained on both therapies throughout treatment, indicating that despite the longer treatment duration with T-DXd versus T-DM1, health-related QoL did not worsen on T-DXd. Furthermore, TDD hazard ratios numerically favored T-DXd over T-DM1 in all prespecified variables of interest including pain, suggesting T-DXd may delay time until health-related QoL deterioration compared with T-DM1. Median time to first hospitalization was three times longer with T-DXd versus T-DM1. Together with reported improved efficacy and manageable toxicity, these results support the overall benefit of T-DXd for patients with HER2+ metastatic breast cancer.

Structures of the HER2-HER3-NRG1ß complex reveal a dynamic dimer interface.

Human epidermal growth factor receptor 2 (HER2) and HER3 form a potent pro-oncogenic heterocomplex1-3 upon binding of growth factor neuregulin-1ß (NRG1ß). The mechanism by which HER2 and HER3 interact remains unknown in the absence of any structures of the complex. Here we isolated the NRG1ß-bound near full-length HER2-HER3 dimer and, using cryo-electron microscopy, reconstructed the extracellulardomain module, revealing unexpected dynamics at the HER2-HER3 dimerization interface. We show that the dimerization arm of NRG1ß-bound HER3 is unresolved because the apo HER2 monomer does not undergo a ligand-induced conformational change needed to establish a HER3 dimerization arm-binding pocket. In a structure of the oncogenic extracellular domain mutant HER2(S310F), we observe a compensatory interaction with the HER3 dimerization arm that stabilizes the dimerization interface. Both HER2-HER3 and HER2(S310F)-HER3 retain the capacity to bind to the HER2-directed therapeutic antibody trastuzumab, but the mutant complex does not bind to pertuzumab. Our structure of the HER2(S310F)-HER3-NRG1ß-trastuzumab Fab complex reveals that the receptor dimer undergoes a conformational change to accommodate trastuzumab. Thus, similar to oncogenic mutations, therapeutic agents exploit the intrinsic dynamics of the HER2-HER3 heterodimer. The unique features of a singly liganded HER2-HER3 heterodimer underscore the allosteric sensing of ligand occupancy by the dimerization interface and explain why extracellular domains of HER2 do not homo-associate via a canonical active dimer interface.

Cryo-EM Structure of HER2-trastuzumab-pertuzumab complex.

Trastuzumab and pertuzumab are monoclonal antibodies that bind to distinct subdomains of the extracellular domain of human epidermal growth factor receptor 2 (HER2). Adding these monoclonal antibodies to the treatment regimen of HER2-positive breast cancer has changed the paradigm for treatment in that form of cancer. Synergistic activity has been observed with the combination of these two antibodies leading to hypotheses regarding the mechanism(s) and to the development of bispecific antibodies to maximize the clinical effect further. Although the individual crystal structures of HER2-trastuzumab and HER2-pertuzumab revealed the distinct binding sites and provided the structural basis for their anti-tumor activities, detailed structural information on the HER2-trastuzumab-pertuzumab complex has been elusive. Here we present the cryo-EM structure of HER2-trastuzumab-pertuzumab at 4.36 Å resolution. Comparison with the binary complexes reveals no cooperative interaction between trastuzumab and pertuzumab, and provides key insights into the design of novel, high-avidity bispecific molecules with potentially greater clinical efficacy.