FCN-437c + letrozole + anastrozole + goserelin acetate

This is a combination therapy consisting of four agents: - **FCN-437c** is an oral, potent, and highly selective second-generation small molecule inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), developed for the treatment of hormone receptor-positive (HR+), HER2-negative advanced or metastatic breast cancer. It blocks cell cycle progression by inhibiting CDK4/6-mediated phosphorylation of the retinoblastoma protein, thereby arresting tumor cell growth[1][2][3][5][7][9]. - **Letrozole** and **anastrozole** are non-steroidal aromatase inhibitors that suppress estrogen biosynthesis by inhibiting the aromatase enzyme, leading to reduced estrogen levels in postmenopausal women. Both are standard-of-care endocrine therapies for HR+ breast cancer[6][10]. - **Goserelin acetate** is a synthetic luteinizing hormone-releasing hormone (LHRH) agonist that suppresses ovarian function and reduces circulating estrogen levels through downregulation of pituitary gonadotropins. The combination targets multiple points in the hormonal signaling pathway to maximize suppression of tumor proliferation in HR+ breast cancer.