sirolimus (albumin-bound) + palbociclib + fulvestrant

This is a **combination regimen** composed of **sirolimus (albumin-bound)**, **palbociclib**, and **fulvestrant**. - **Sirolimus (albumin-bound)**, known as a nanoparticle albumin-bound formulation, is an mTOR (mechanistic target of rapamycin) inhibitor with antineoplastic and immunosuppressive activity. Albumin-bound sirolimus allows intravenous administration, potentially improving tumor penetration and overcoming the low water solubility of standard sirolimus. - **Palbociclib** is an orally available, small molecule inhibitor of cyclin-dependent kinase 4 and 6 (CDK4/6), blocking cell cycle progression from G1 to S phase, thereby inhibiting cancer cell proliferation. - **Fulvestrant** is a selective estrogen receptor degrader (SERD) that acts as an antagonist to estrogen receptors and leads to their degradation, used mainly in hormone receptor (HR)-positive breast cancer. This combination is being studied for advanced hormone receptor-positive, HER2-negative breast cancer, particularly in populations resistant to (neo)adjuvant endocrine therapy[1][3].