abemaciclib + goserelin + letrozole + trastuzumab

This is a four-drug combination regimen consisting of abemaciclib, goserelin, letrozole, and trastuzumab. It is used as a non-chemotherapy treatment strategy for patients with HER2-positive and hormone receptor (HR)-positive metastatic breast cancer, particularly in premenopausal women. - **Abemaciclib** is an oral small molecule inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), which blocks cell cycle progression in cancer cells. - **Goserelin** is a luteinizing hormone-releasing hormone (LHRH) agonist that suppresses ovarian function to reduce estrogen production. - **Letrozole** is an aromatase inhibitor that further reduces estrogen synthesis by blocking the conversion of androgens to estrogens. - **Trastuzumab** is a monoclonal antibody targeting the human epidermal growth factor receptor 2 (HER2), inhibiting proliferation of HER2-overexpressing tumor cells. This combination aims to simultaneously block cell cycle progression, suppress estrogen-driven signaling, and inhibit HER2-mediated pathways. Clinical evidence suggests it can provide durable responses with manageable toxicity profiles in selected patient populations[1][6][7].