trastuzumab deruxtecan + paclitaxel + trastuzumab + pertuzumab

This is a **combination regimen** composed of four agents: **trastuzumab deruxtecan**, **paclitaxel**, **trastuzumab**, and **pertuzumab**. - **Trastuzumab deruxtecan** is an antibody-drug conjugate targeting HER2 (human epidermal growth factor receptor 2), delivering a cytotoxic topoisomerase I inhibitor payload specifically to HER2-expressing cells. - **Paclitaxel** is a taxane-class microtubule inhibitor used as chemotherapy. - **Trastuzumab** and **pertuzumab** are both monoclonal antibodies directed against different domains of HER2, together providing dual blockade and enhancing antitumor activity through inhibition of proliferation, induction of ADCC (antibody-dependent cellular cytotoxicity), and complement-mediated cytotoxic effects[4]. This combination represents an investigational or off-label use (distinct from standard-of-care combinations) and may be studied in clinical trials as an experimental regimen for **HER2-positive metastatic breast cancer**.