Abstract OT1-02-01: Phase I trial of bicalutamide and ribociclib in androgen receptor-positive triple negative breast cancer

Abstract

Abstract Background: To date, the use of anti-androgens in the subset of triple negative breast cancers (TNBC) that express androgen receptor (AR) has shown modest response rates, indicating anti-androgen-resistance in the majority of these tumors. Based on data that Cyclin D kinase (CDK) inhibitors reverse resistance to anti-androgens in prostate cancer cell lines, we hypothesize that the use of CDK inhibition may enhance the activity of anti-androgens in AR-positive TNBC. Methods: Key eligibility include: patients with centrally confirmed AR-positive TNBC, defined as AR expression >0%; 0 to 1 line of prior therapy for metastatic disease; and measurable disease. Patients are treated with bicalutamide 150mg orally once daily plus ribociclib at one of 3 dose levels (see table). Table 1Dose levelBicalutamideRibociclib1150mg orally once daily (D1 to 28)400mg daily (D1 to 21)2150mg orally once daily (D1 to 28)400mg daily (D1 to 28)3150mg orally once daily (D1 to 28)600mg daily (D1 to 21) Results: AR expression was positive by trial criteria in 74% of screened patients. Three patients have been accrued at each dose level. Median age is 56 and 6 and 3 patients were treated in first and second-line settings, respectively. Median AR expression was 50% (range 5 to 75%). Toxicity data is available for 6-patients treated on dose levels 1 and 2. No dose-limiting toxicities were noted. As anticipated with ribociclib, the most common toxicity is neutropenia (1 patient grade 4 and 2 patients grade 3). Two patients experienced grade 3 hypertension and 1 experienced grade 3 lymphopenia. Grade 2 or lower toxicities included fatigue, nausea, hyperglycemia and mucositis. One patient experienced grade 1 QT interval prolongation. Conclusion: The combination of bicalutamide and ribociclib is tolerable without unexpected toxicities. Data on the 3-patients treated at dose level 3 and dose expansion will be included. Phase 2 dosing schedule will be decided based on phase 1 results. Citation Format: Sharifi M, Wisinski KB, Burkard ME, Tevaarwerk AJ, Tamkus D, Chan N, Truica C, Danciu O, Hoskins K, O'Regan RM. Phase I trial of bicalutamide and ribociclib in androgen receptor-positive triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT1-02-01.