A Randomized Phase Ii Trial Of Fulvestrant With Or Without Ribociclib After Progression On Aromatase Inhibition Plus Cyclin-Dependent Kinase 4/6 Inhibition In Patients With Unresectable Or Metastatic Hormone Receptor Positive, Her2 Negative Breast Cancer

TPS1112Background: CDK4/6i, including palbociclib and ribociclib (R), have demonstrated remarkable benefit in progression free survival (PFS) in patients (pts) with HR+, HER2- MBC with anti-estrogen therapy. Switching between anti-estrogen therapies at disease progression is standard of care in the treatment of HR+ MBC. We evaluate the strategy of switching anti-estrogen therapy to fulvestrant (F) and maintaining CDK4/6 inhibition with R in pts with HR+, HER2- MBC who have progressed on an AI + CDK4/6i. Methods: Trial Design Phase II, multi-center, randomized, double-blind, placebo-controlled trial to evaluate F +/- R in pts with HR+, HER2- MBC who have previously progressed on any AI + CDK4/6i: Screened at 2 different scenarios: Scenario 1: Before receiving any CDK4/6i Scenario 2: Time of progression of disease (POD) while being treated with an AI + CDK4/6i Intervention At randomization, pts assigned 1:1 to either a) F + R or b) F + placebo, with treatment given in 4-week cycles. Major Eligibility Criter...