Abstract P1-19-31: 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: Results of the third interim analysis

Introduction: RIBECCA is a national, multi-center, open-label, single-arm phase IIIb trial assessing the efficacy and safety of ribociclib in combination with letrozole in a patient population similar to the populations of MONALEESA-2, -3 and -7. Here we present the results of the third preplanned interim analysis. Methods: Main inclusion criteria allowed enrollment of men or women with metastatic or locally advanced breast cancer not amenable to curative treatment by surgery or radiotherapy, and histological or cytological confirmation of HR+, HER2- breast cancer, irrespective of their menopausal status. The primary objective is to assess the clinical benefit rate (CBR) after 6 months. Secondary objectives include: progression free survival (PFS), overall survival (OS), safety and changes in quality of life. Here we describe a preliminary analysis baseline characteristics, safety data and the clinical benefit rate (CBR) at 24 weeks, of all enrolled patients (n=502). Results: The cut-off date for this third interim analysis was 6 months after the last patient was enrolled in the study. The median observation time for all patients in this analysis was 9.4 months (0.1-26.0 months). Baseline characteristics: of 502 pts, 497 were female and 5 male. Median age: 64 yrs; 46 pts pre-or perimenopausal, 451 postmenopausal (missing: 5); ECOG 0-1: 96.8%; median time since first recurrence: 1.6 months; 71.1 % of pts had bone metastases (40.8% bone only), 30.1% liver, 28.1% lung and 30.1% other metastases. Median relative dose intensity was 0.90 for ribociclib and 1 for letrozole. The most common treatment emergent AEs (all grades) were neutropenia and/or neutrophil count decreased (57.8%), nausea (41.2%), fatigue (37.5%), alopecia (34.5%), leukopenia or WBC decreased (29.7%), nasopharyngitis (24.7%), diarrhea (23.5%), ALT increased (21.5%) and AST increased (19.7%). The CBR by week 24 was 69.2%. Conclusion: The results of the third interim analysis confirmed clinical benefit in this patient population. No new safety signals were detected. This is in line with data published from the pivotal phase III studies MONALEESA-2, MONALEESA-3 and MONALEESA-7. Citation Format: Andreas Hartkopf, Arnd Nusch, Thomas Decker, Mattea Reinisch, Bernhard J Heinrich, Christian Kurbacher, Roswitha Fuchs, Hans Tesch, Petra Krabisch, Sara Brucker, Tanja N Fehm, Wolfgang Janni, Sherko Kummel, Diana Luftner, Andreas Schneeweiss, Martin H Schuler, Claudia Voges, Jorg Schubert, Peter A Fasching. 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: Results of the third interim analysis [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-19-31.