cyclophosphamide + epirubicin + pyrotinib + trastuzumab

This is a combination regimen used in the treatment of HER2-positive breast cancer. The regimen includes four agents with distinct mechanisms of action: - **Cyclophosphamide**: An alkylating agent that cross-links DNA, leading to cell death. - **Epirubicin**: An anthracycline topoisomerase II inhibitor that intercalates into DNA and inhibits its replication. - **Pyrotinib**: An irreversible pan-HER tyrosine kinase inhibitor (TKI) targeting HER1, HER2, and HER4 receptors, blocking downstream signaling pathways[2]. - **Trastuzumab**: A monoclonal antibody targeting the extracellular domain of the HER2 receptor, inhibiting cell proliferation and inducing antibody-dependent cellular cytotoxicity (ADCC)[1][4]. The combination is designed to maximize antitumor efficacy by simultaneously targeting multiple pathways critical for cancer cell survival and proliferation. Clinical studies have shown that combinations including pyrotinib and trastuzumab significantly improve progression-free survival in patients with untreated or heavily pre-treated HER2-positive metastatic breast cancer[1][4].