Abstract OT2-01-05: TRINITI-1: Ribociclib + everolimus (EVE) + exemestane (EXE) triplet combination in men or postmenopausal women with HR+, HER2– advanced breast cancer (ABC) following progression on a cyclin-dependent kinase (CDK) 4/6 inhibitor

Abstract

Abstract Background: There is extensive crosstalk between the cyclin D–CDK4/6–inhibitor of CDK4–retinoblastoma and phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathways at the G1/S cell-cycle checkpoint. Both pathways are frequently dysregulated in hormone receptor-positive (HR+) breast cancer and have been associated with endocrine therapy (ET) resistance. CDK4/6 and PI3K/mTOR inhibitors have demonstrated clinical activity in combination with ET. Although CDK4/6 inhibitors combined with ET significantly improve progression-free survival (PFS) in ABC, disease progression eventually occurs, highlighting the need for effective treatment options following doublet therapy. Ribociclib (LEE011; CDK4/6 inhibitor; 3-weeks-on/1-week-off) + EVE (mTOR inhibitor) + EXE triplet therapy has shown preliminary clinical activity in heavily pretreated HR+, human epidermal growth factor receptor 2-negative (HER2–) ABC including patients (pts) with prior exposure to CDK4/6 inhibitors, suggesting this combination may restore sensitivity to CDK4/6 inhibitor-based therapy. Trial design and objectives: TRINITI-1 (NCT02732119) is a US-based, phase I/II, single arm, open-label study of ribociclib (continuous daily dosing) + EVE (2.5 mg/day) + EXE (25 mg/day) in men and postmenopausal women with HR+, HER2– ABC refractory to ≥1 line of ET. Phase I dose escalation consists of 2 ribociclib dose-level cohorts (250 and 300 mg/day), followed by a Simon Two-Stage phase II trial in pts with disease progression on prior CDK4/6 inhibitor-based therapy. No more than 3 lines of therapy for ABC, including ≤1 prior chemotherapy regimen, are permitted. Previous EXE treatment of >28 days for metastatic disease, prior mTOR inhibitors, and progression on >1 CDK4/6 inhibitor are prohibited. All pts in phase II must have progressed on a CDK4/6 inhibitor as the last regimen before study entry. Additional eligibility criteria include measurable disease or lytic/mixed bone lesions and Eastern Cooperative Oncology Group performance status of ≤1. Exclusion criteria include visceral crisis, unstable CNS metastases, and clinically significant heart disease. Phase I primary objective: maximum tolerated dose and/or recommended phase II dose of the triplet combination. Phase II primary objective: clinical benefit rate (CBR) at 24 weeks (0.1 significance level, 80% power to test CBR ≤15% against CBR ≥30%) with centrally-assessed PFS as a key secondary objective. Other secondary objectives include preliminary antitumor activity (phase I), safety and pharmacokinetics (phase I/II), and overall response rate, overall survival, and duration of overall response (phase II). Tumor assessments (RECIST v1.1) will be performed every 8 weeks for the first 12 months, and every 12 weeks thereafter until disease progression. Exploratory analyses include biomarkers potentially predictive of response and mechanisms of resistance. Target accrual: Approximately 52 pts at ∼30 sites; 3–6 pts per cohort in phase I, an initial 19 in phase II with another 20 enrolled upon demonstration of clinical benefit in ≥4 pts. Citation Format: Bardia A, Hurvitz S, Yardley DA, Zelnak A, DeMichele A, Clark AS, Warsi G, Small T, Tucci C, Moulder S. TRINITI-1: Ribociclib + everolimus (EVE) + exemestane (EXE) triplet combination in men or postmenopausal women with HR+, HER2– advanced breast cancer (ABC) following progression on a cyclin-dependent kinase (CDK) 4/6 inhibitor [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 OT2-01-05.