letrozole + palbociclib + pembrolizumab

This is a combination therapy consisting of three agents—letrozole, palbociclib, and pembrolizumab—used in the treatment of hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) metastatic breast cancer. Letrozole is an aromatase inhibitor that reduces estrogen production, thereby limiting the growth stimulus for estrogen-dependent breast cancer cells. Palbociclib is a small molecule inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), which blocks cell cycle progression from G1 to S phase, inhibiting tumor cell proliferation. Pembrolizumab is a monoclonal antibody immune checkpoint inhibitor targeting programmed death-1 (PD-1) on T cells; it enhances anti-tumor immune responses by preventing PD-1-mediated inhibition of T-cell activity. The combination aims to leverage endocrine therapy with targeted cell cycle inhibition and immunotherapy for synergistic anti-cancer effects[1][2].