xentuzumab + abemaciclib + letrozole

This is a **combination investigational therapy** comprising xentuzumab (a humanized monoclonal antibody targeting insulin-like growth factor [IGF] ligands 1 and 2), abemaciclib (a small molecule inhibitor of cyclin-dependent kinases CDK4 and CDK6), and letrozole (a non-steroidal aromatase inhibitor), studied primarily for the treatment of advanced hormone receptor-positive, HER2-negative breast cancer. - **Xentuzumab** binds to IGF-1 and IGF-2, blocking their interaction with the IGF-1 receptor as well as IGF-2's interaction with insulin receptor variant A, thereby inhibiting the IGF signaling pathway, which is implicated in tumor cell proliferation and resistance mechanisms. - **Abemaciclib** inhibits CDK4/6, blocking cell cycle progression in tumor cells. - **Letrozole** suppresses estrogen biosynthesis by inhibiting the aromatase enzyme, reducing tumor growth in hormone-dependent cancers. The combination is being evaluated for its potential to overcome resistance mechanisms in hormone receptor-positive, HER2-negative advanced/metastatic breast cancer by simultaneously inhibiting estrogen-driven, IGF-driven, and cell-cycle pathways[1][2][3][5][7].