Abstract PO5-20-04: A Phase II Study of Ribociclib and Endocrine Treatment of Physician’s Choice for Locoregional Recurrent, Resected Hormone Receptor Positive HER2 Negative Breast Cancer (RaPhLRR Study)

Abstract Background Hormone receptor positive (HR+) breast cancer (BC) is the most common subtype of BC (70-80%). This subset tends to have good prognosis, therefore most patients with localized disease have excellent long-term survival, approaching 100% 5-year relative survival. However, 10% of patients experience loco-regional recurrence (LRR) within 5 year of final surgical management of the primary disease-well within the typical treatment window of adjuvant endocrine therapy. Few studies exists to guide the systemic treatment of patients who have suffered LRR of HR+ HER2 - BC. The randomized controlled CALOR trial demonstrated no benefit to systemic cytotoxic chemotherapy for this subgroup of patients and persistent high rate of subsequent recurrences (50% within 10 years on LRR event). There is no standard of care for managing this patient population. The combination of ribociclib and endocrine therapy (ET) (fulvestrant and aromatase inhibitors) is FDA approved for management of unresectable recurrences and metastatic HR+HER- BC (MONALEESA trials). CDK4/6 inhibitors have been investigated in early BC setting too, several trials showing positive results (monarchE, NATALEE). Data is needed to investigate their use in patients with LRR. Trial design This is a multicenter, single arm phase II study to evaluate efficacy and safety of ribociclib and ET in patients with LRR of HR+HER2- BC. Treatment includes ribociclib for 36 months, 600 mg daily for 21 days, 28-day cycle plus physician’s choice ET for 60 months (fulvestrant or AIs). Ribociclib dose was chosen based on approved dose in metastatic BC. Eligibility Criteria Patients ≥ 18 of age, with LRR of BC (ipsilateral breast, axilla, regional lymph nodes, chest wall), histologically confirmed estrogen receptor positive and/or progesterone receptor positive, HER 2 negative. Patients must have adequate local treatment for LRR (surgery and/or radiation) with negative microscopic margins, no evidence of distant metastatic disease. Prior treatment with neo-adjuvant and adjuvant chemotherapy and ET is allowed, no prior CDK 4/6 inhibitor in the last 12 months. Pre and post-menopausal women are allowed. Patient must enroll within 6 months of the last local therapy. Specific aims Primary objective: to estimate subsequent recurrence-free survival (RFS) at 3 years for ribociclib when administered with ET in patients with HR + HER2- BC with adequately resected local recurrence. Secondary objectives: to estimate distant metastasis-free survival and overall survival, to evaluate safety and tolerability, to identify predictors of LRR. Correlative analysis will explore prognostic and predictive biomarkers of treatment with ribociclib and ET and potential molecular mechanisms of resistance to treatment. Statistical Methods From previous published data (J Clin Oncol. 2018 Apr 10;36(11):1073-1079), we assume that patients receiving standard of-care management following recurrence would have a recurrence free survival (RFS) rate of 80% at 3 years and that treatment with ribociclib + ET will increase it by 7%. We wish to have at least 80% power at that significance level of 0.0487 to correctly detect that improvement in RFS rate at 3 years from 80 to 87%. Because only an improvement in RFS rate is of clinical interest, we have a directional hypothesis, and have used a 1-sided alpha. Using a one-sample survival study design, with assumed accrual duration of 3-years and additional follow-up time of 3 years, the minimum sample size requirement is N=180 patients. Target accrual The minimum sample size requirement is N=180 patients. A bigger sample size of N=200 patients will achieve a power of at least 84%. Current accrual is 6/200. This study will be open at up to 35 sites. Contact information The study is being administered through the HCRN, it can be identified as BRE20-468, NCT05467891, ocdanciu@uic.edu Citation Format: Oana Danciu, Nancy Chan, Kari Wisinski, Trish Millard, Kathleen Kemmer, Sneha Phadke, Zhengjia Chen, Ana Cuesta Fernandez, Melanie Clark, Alison Conlin, Coral Omene, Sima Ehsani, Stephanie Dublis, Vijayakrishna K. Gadi. A Phase II Study of Ribociclib and Endocrine Treatment of Physician’s Choice for Locoregional Recurrent, Resected Hormone Receptor Positive HER2 Negative Breast Cancer (RaPhLRR Study) abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-20-04.