The DESTINY-Breast04 study [4] was performed as an open-label randomized phase 3 study comparing T-DXd and a treatment of physician’s choice (TPC) (capecitabine, eribulin, gemcitabine, paclitaxel, or albumin-bound paclitaxel) in 557 patients with unresectable or metastatic HER2-low breast cancer who underwent chemotherapy with 1 or 2 regimens in the metastatic setting. This evidence concerns the gene ERBB2 and breast carcinoma.