SPH4336 + letrozole

**SPH4336 + letrozole** is an investigational oral combination therapy comprising **SPH4336**, a highly selective, novel cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor, and **letrozole**, an established nonsteroidal aromatase inhibitor. The combination is being studied for the first-line treatment of hormone receptor-positive, HER2-negative, locally advanced or metastatic breast cancer. SPH4336 functions by inhibiting CDK4/6, leading to suppression of cell cycle progression in cancer cells, while letrozole reduces estrogen synthesis, further decreasing the proliferative drive in estrogen receptor-positive tumor cells. This combination is intended to overcome or delay resistance to endocrine therapy and CDK4/6 inhibitors[3][4][5].