12. This was defined in the DESTINY-Breast04 study as tumors expressing an immunohistochemical score of 1+, or 2+ without gene amplification by ISH. The randomized, multicenter, open-label clinical trial involved 557 patients with unresectable or metastatic HER2 low breast cancer, who after receiving targeted therapy showed improvement in overall and progression-free survival. The Food and Drug Administration (FDA) approved Trastuzumab-deruxtecan (T-Dxd) therapy in this subgroup in August 2022 11,.13 Here, ERBB2 is linked to breast cancer.