This clinical trial studies treatments for hormone receptor-positive breast cancer that has spread to other parts of the body (advanced or metastatic). The study compares two different treatment strategies using medications called CDK4/6 inhibitors (including abemaciclib, palbociclib, and ribociclib) combined with hormone therapy. These medications work by blocking proteins that help cancer cells grow.
The main purpose is to determine which treatment sequence works better: using a CDK4/6 inhibitor with hormone therapy first, followed by fulvestrant alone when the disease progresses; or starting with hormone therapy alone, followed by fulvestrant combined with a CDK4/6 inhibitor when the disease progresses. Additional hormone therapies that may be used include anastrozole, letrozole, goserelin, and leuprorelin.
During the study, patients will receive treatment until their disease progresses or they cannot tolerate the medication. The researchers will monitor how long it takes for the cancer to progress after both first and second treatments, overall survival, quality of life, and side effects. They will also collect tumor samples and blood tests to study markers that might help predict which patients respond best to treatment.



The Netherlands