The double blind, placebo-controlled MONALEESA-2 trial met its primary endpoint of clinically meaningful improvement in PFS at the pre-planned interim analysis for the combinatorial treatment of the cyclin-dependent kinase (CDK) 4/6-Inhibitor ribociclib and letrozole vs. letrozole monotherapy for postmenopausal, estrogen receptor positive (ER+), human epidermal growth factor receptor 2-negative (HER2-) women who were naïve to treatment for advanced disease.

Here we present the national, multi-center, open-label, single-arm phase IIIb trial RIBECCA assessing the efficacy and safety of the combination of ribociclib and letrozole in an additional population, accompanied by a set of exploratory objectives.


Main inclusion criteria allow enrollment of women with metastatic or locally advanced breast cancer not amenable to curative treatment by surgery or radiotherapy, and histological or cytological confirmation of ER+, HER2- breast cancer, irrespective of their menopausal status.

The primary objective is to assess the Clinical Benefit Rate (CBR) after 6 months, the secondary objectives include progression free survival (PFS), overall survival (OS), safety and change in quality of life.

The exploratory objectives include the assessment of biomarkers (e.g. ctDNA, CTCs, miRNA) predictive for response and the occurrence of adverse events of special interest. The influence of CDK4/6-inhibition on the immune system will be another exploratory endpoint of this study.


With a planned recruitment of 500 patients in about 100 trial sites the RIBECCA trial will contribute to a better understanding of the safety, efficacy and possibly mechanisms related to CDK4/6-inhibition through ribociclib.

Citation Format: Fasching PA, Decker T, Fehm T, Janni W, Kuemmel S, Lueftner D, Schneeweiss A, Schuler M, Guderian G, Schmidt-Wetzel S, Reiners R, Schubert J, Brucker S. RIBECCA - A phase IIIb, multi-center, open label study for women with estrogen receptor positive locally advanced or metastatic breast cancer treated with ribociclib (LEE011) in combination with letrozole [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr OT2-01-18.