capecitabine + dalpiciclib + pyrotinib

This is an investigational oral combination therapy consisting of three small molecule drugs—capecitabine, dalpiciclib, and pyrotinib—being studied primarily for the treatment of HER2-positive advanced or metastatic breast cancer. - **Capecitabine** is a prodrug that is enzymatically converted to 5-fluorouracil (5-FU) in the body and acts as an antimetabolite inhibiting DNA synthesis in rapidly dividing tumor cells. - **Dalpiciclib** is a selective cyclin-dependent kinase 4/6 (CDK4/6) inhibitor that blocks cell cycle progression from G1 to S phase by inhibiting phosphorylation of retinoblastoma protein, thereby suppressing tumor cell proliferation. - **Pyrotinib** is an irreversible pan-ErbB receptor tyrosine kinase inhibitor targeting HER1 (EGFR), HER2, and HER4 receptors; it inhibits downstream signaling pathways critical for tumor growth and survival. The rationale for combining these agents lies in their complementary mechanisms targeting different aspects of breast cancer biology—HER2 signaling inhibition by pyrotinib, cell cycle arrest by dalpiciclib, and cytotoxicity via capecitabine. This combination aims to improve efficacy over single-agent or dual-agent regimens in patients with HER2-positive metastatic breast cancer[3][4][10].