The BEGONIA platform trial is evaluating durvalumab plus trastuzumab deruxtecan as a first-line regimen for HER2-low metastatic breast cancer, with the report highlighting unusually deep and durable tumor responses in early-phase results. Trastuzumab deruxtecan pairs a HER2-directed antibody with a chemotherapy payload delivered through an antibody-drug conjugate mechanism. Durvalumab adds immune checkpoint inhibition, and the trial’s positioning in a first-treatment setting suggests investigators are aiming to combine direct tumor cytotoxicity with immune activation rather than sequencing these modalities later. For development teams, BEGONIA serves as another proof point that HER2-low biology is being actively reclassified through combination oncology strategies, with response durability becoming a primary differentiator in next-line competitive landscapes.