fulvestrant + palbociclib or ribociclib

This refers to a **combination regimen** used in oncology, where **fulvestrant** (a selective estrogen receptor degrader) is given in combination with either **palbociclib** or **ribociclib** (both cyclin-dependent kinase 4/6 inhibitors) for the treatment of **hormone receptor-positive, HER2-negative advanced or metastatic breast cancer**. Fulvestrant acts as an estrogen receptor antagonist that accelerates degradation of the estrogen receptor, effectively blocking estrogen-driven tumor growth. Palbociclib and ribociclib are selective inhibitors of the cyclin-dependent kinases CDK4 and CDK6, blocking cell cycle progression at the G1/S checkpoint, thus inhibiting cancer cell proliferation. This combination improves progression-free survival and is approved for breast cancer that has progressed after endocrine therapy[1][2][3][5].