ASCO 2022: Endocrine Therapy Plus Ribociclib for CDK4/6 Inhibitor–Resistant Metastatic Breast Cancer

By: Vanessa A. Carter, BS
Posted: Thursday, June 16, 2022

Kevin Kalinsky, MD, of Winship Cancer Institute, Emory University, Atlanta, and colleagues assessed whether endocrine therapy with fulvestrant or exemestane with or without ribociclib would improve outcomes in patients with unresectable or hormone receptor–positive, HER2-negative metastatic breast cancer. During the 2022 American Society of Clinical Oncology (ASCO) Annual Meeting (Abstract LBA1004), the results from the phase II MAINTAIN TRIAL demonstrated a significant progression-free survival benefit for those switching to endocrine therapy plus ribociclib after disease progression on CDK4/6 inhibitor therapy.

“While observational data demonstrate a potential benefit of continuing CDK4/6 inhibitors and switching endocrine therapy at progression, no prospective trials have evaluated this approach,” mentioned the investigators.

The trial enrolled 120 patients with hormone receptor–positive, HER2-negative metastatic breast cancer whose disease progressed on CDK4/6 inhibitors and endocrine therapy. Participants were randomly assigned to receive fulvestrant or exemestane with ribociclib or placebo; individuals treated with prior exemestane received fulvestrant and vice versa and those administered neither regimen were assigned per investigator discretion.

The median patient age was 57 years, with a majority of participants identifying as White (74%). Approximately 83% of patients received fulvestrant as a prior endocrine therapy, and prior CDK4/6 inhibitors included palbociclib (84%), ribociclib (11%), abemaciclib (2%), and other (3%).

Among individuals who received fulvestrant or exemestane with ribociclib, there was a statistically significant improvement in progression-free survival when compared with those receiving placebo (P = .004). Of note, the median progression-free survival was also significantly higher in patients given fulvestrant and ribociclib versus placebo (P = .02). At the 6-month mark, 42% and 24% were progression-free in the ribociclib and placebo arms, respectively; the 12-month rates were 25% and 7%.

Disclosure: For full disclosures of the study authors, visit coi.asco.org.

2022 ASCO Annual Meeting

---