ORACLE-RIPA study: A phase II, randomized, open-label, parallel-group study comparing the immune modulation effect of neoadjuvant ribociclib, palbociclib, and abemaciclib in early ER+/HER2- breast cancer.

Abstract

TPS632 Background: CDK4/6 inhibitors (CDK4/6i), ribociclib, palbociclib, and abemaciclib, provide similar progression-free survival (PFS) benefits when combined with endocrine therapy in ER+/HER2- metastatic breast cancer (MBC) patients. However, not all CDK4/6i have demonstrated overall-survival (OS) benefits in their respective phase III trials. Both, ribociclib and abemaciclib, have shown significant OS benefits in ER+/HER2- MBC patients, but palbociclib has not. Because of similar benefits of the 3 CDK4/6i on PFS, the OS benefit is likely not a result of differences in their synergistic efficacy of a CDK4/6i with endocrine therapy. CDK4 inhibition on cancer cells can also result in upregulation of MHC-I and MHC-II expression on cell surface and Rb-dependent interferon-gamma secretion. CDK6 inhibition might inhibit T cell and NK cell proliferation causing a negative effect on the tumor microenvironment. CDK6 inhibition can also reduce regulatory T cell numbers and increase cytokine production to enhance cytotoxic T cell function. Thus, we hypothesize that the differential impact of the 3 CDK4/6i on OS might be resulting from different immunomodulation effects. To investigate the functional alterations of the CDK4/6i on the BC microenvironment, the neoadjuvant treatment setting is best to compare the immune modulation effects of CDK4/6i from pre-treatment and post-treatment tumor tissues. Methods: This phase II multicenter, randomized, open-label, parallel-group study evaluates the immunomodulation effects of the 3 different CDK4/6i (ribociclib, palbociclib, or abemaciclib) combined with letrozole in neoadjuvant early ER+/HER2- breast cancer patients. A total of 20 patients will be enrolled into each treatment arm. The major inclusion criteria are female patients aged ≥ 20 years old, having a histologically and/or cytologically confirmed diagnosis of ER+ ( > 10%) and/or PR+, HER2 negative (IHC 0+/1+, or IHC 2+ plus FISH negative) breast cancer, stage II/III, and adequate organ function. The treatment will12 weeks of letrozole plus a CDK4/6i. Premenopausal patients will receive GnRH agonist. Breast tumor biopsy, blood and stool samples will be collected prospectively at the time prior to treatment initiation, at 2 weeks after treatment, and at surgery. A description summary will be utilized to compare the results between the 3 CDK4/6i. The trial results will address questions about differences or similarities of the 3 CDK4/6i within the same study. The study is currently enrolling at 3 medical centers s in Taiwan. Clinical trial information: Pending formal number assignment .