This clinical trial focuses on treating metastatic breast cancer in postmenopausal women whose cancer is hormone receptor-positive and HER2-negative. These specific characteristics mean that the cancer cells are influenced by hormones but do not have high levels of a protein called HER2. The study examines the effectiveness of combining two medications: fulvestrant (Faslodex), which is given by injection under the skin, and palbociclib, which is taken as oral capsules.

The purpose of this research is to compare how well fulvestrant works when given alone with placebo versus when it is combined with palbociclib. The study specifically looks at how long patients remain free from disease progression during treatment. This research includes women who have previously received at least 5 years of hormone therapy and remained disease-free for more than 12 months after completing that treatment, or women who were diagnosed with metastatic disease from the beginning.

During the study, participants receive either fulvestrant with palbociclib or fulvestrant with placebo. Fulvestrant is administered as a 500 mg injection, while palbociclib is taken as a 125 mg daily capsule. The treatment continues for up to 480 days, during which doctors monitor the cancer’s response to treatment and check for any side effects. Throughout the study, participants undergo regular medical examinations and imaging tests to evaluate how the disease responds to treatment.