Abstract PS10-31: Ribecca - a phase 3b, 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: Final results

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, including premenopausal and postmenopausal patients without pretreatment as well as patients with up to 3 previous treatment lines for advanced disease. Here we present the final analysis for the primary endpoint. Methods:The study enrolled women or men with metastatic or locally advanced breast cancer irrespective of their menopausal status, who were not amenable to curative treatment by surgery or radiotherapy. Histological or cytological confirmation of HR+, HER2- breast cancer was required. 502 patients were enrolled in two Cohorts. Cohort A (n=319): postmenopausal women and men without pretreatment for advanced disease; Cohort B (n=183): premenopausal women without pretreatment for advanced disease and pre- or postmenopausal women and men with ≤ 1 line of chemotherapy and/or ≤ 2 lines of endocrine therapy in the advanced situation. The primary endpoint was to assess the clinical benefit rate (CBR, defined as CR, PR or SD, or NCRNPD) at 24 weeks for the overall study population. Secondary endpoints included: progression free survival (PFS), overall survival (OS), safety, and changes in quality of life as assessed by EORTC QLQ-C30 and -BR23 questionnaires. Results: The study ended 84 weeks after the enrollment of the last patient. The median observation time was 10.6 months (0.1-38 months). Baseline characteristics: of 502 pts, 5 were male, 497 were female(46 pre-or perimenopausal, 451 postmenopausal); median age: 64 yrs; ECOG 0-1: 96.8%; 71.1 % of pts had bone metastases (40.8% bone only), 30.6% liver, 27.5% lung and 30.1% other metastases. 97.3% had at least 1 metastatic site: 48.7% had 1, 35.1% had 2, 12.9% had 3 and 1.6% had 4 metastatic sites, respectively. 78.9% received at least one prior antineoplastic therapy: 4.9% received neoadjuvant, 56.8% adjuvant and 37.8% palliative treatment as last antineoplastic therapy before study start. The most common treatment emergent AEs (all grades) were neutropenia and/or neutrophil count decreased (60.6%), nausea (42%), fatigue (39.2%), alopecia (35.1%), leukopenia or WBC decreased (30.7%), nasopharyngitis (28.5%), diarrhea (25.3%), ALT increased (22.9%) and AST increased (20.7%). The CBR at week 24 for the overall study population was 69.2%. Median PFS was 16.5 [95%CI 13.7; 19.3] months in the overall study population, 21.8 [15.4; 25.3] months and 9.3 [8.1; 16.3] months in Cohort A and B, respectively. At 72 weeks, the Kaplan-Meier estimate for OS was 86.8% [83.3; 89.6]. Because of the low number of events during the study period, median OS could not be determined. Conclusion: The results of the final analysis confirmed clinical benefit of ribociclib and letrozole in this patient population. No new safety signals emerged. Citation Format: Mattea Reinisch, Arndt Nusch, Thomas Decker, Andreas Hartkopf, Bernhard J Heinrich, Christian M Kurbacher, Roswitha Fuchs, Hans Tesch, Petra Krabisch, Sara Y Brucker, Tanja Fehm, Wolfgang Janni, Sherko Kuemmel, Diana Luftner, Andreas Schneeweiss, Martin Schuler, Claudia Voges, Joerg Schubert, Peter A Fasching. Ribecca - a phase 3b, 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: Final results [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-31.