Abstract P5-19-22: A phase I clinical trial of entinostat and lapatinib in patients with trastuzumab refractory HER2-positive metastatic breast cancer

Background: Our preclinical data show that entinostat enhances the efficacy of lapatinib in HER2 positive (HER2+) breast cancer cell lines via FOX-03-mediated Bim1 expression. In-vitro and in- vivo, the combination of entinostat and lapatinib enhanced apoptosis in lapatinib-resistant cells. We conducted a phase I study with the primary objective to determine the RP2D of entinostat plus lapatinib in patients with HER2+ metastatic breast cancer with progressive disease (PD) after trastuzumab treatment. Methods: This was a single-center, open-label study to evaluate the dose limiting toxicity (DLT) and determine the MTD of every-other-week entinostat plus daily lapatinib in 28-day cycles. Patients with locally recurrent or metastatic breast cancer in whom trastuzumab had failed were enrolled. DLT was defined as: any toxicity resulting in 14 or more days of treatment delay, febrile neutropenia (NTP), grade 4 NTP for over 7 days, any grade 3 or higher non-hematologic toxicity, grade 3 nausea, vomiting, diarrhea or electrolyte imbalance lasting over 48 hours despite adequate supportive care, or a platelet count less than 10,000. Grading was assigned according to common toxicity criteria (CTC 4). A standard 3+3 dose escalation design was used. Entinostat was given at 10 mg (level 0), 12 mg (level 1), or 15 mg (level 2) by mouth every 14 days. Lapatinib was given at 1250 mg by mouth daily. Toxicity was evaluated on day 15 and day 28 for C1 and C2, and at the end of each cycle thereafter. Results: Fifteen patients with HER2+ metastatic breast cancer were enrolled. Median age was 52 years (range 26-69), median of all prior systemic treatment was 4 (range 1- 12), and median prior trastuzumab-based regimens was 2 (range 1-6). Eight patients had prior lapatinib exposure. Seven patients had ER+/HER2+ tumors. Median number of cycles completed was 2 (range 1-13). DLT was observed in 0 of 3 patients at level 0, 1 of 6 at level 1, and 1 of 6 at level 2. 3 patients at level 1 had lapatinib dose reductions because of grade 3 rash (n=2) or grade 3 dyspnea (n=1) or grade 3 abdominal pain (n=1). 2 patients at level 2 had entinostat dose reductions because of grade 4 NTP in cycle 1 (n=1) or grade 3 NTP in cycle 5 and grade 4 neutropenia in cycle 6 (n=1). Five patients had SD (defined per 2009 RECIST guidelines): two at dose level 1 for 6 months and 13 months, three at level 2 for 3, 4, and 8 months. Median time to progression was 2 months (range 1-13). The most common treatment related adverse events were fatigue (n=15), myalgia (n=14), nausea (n=14), diarrhea (n=13), anemia (n=11), and rash (n=11). Conclusion: MTD was not reached. Cumulative toxicity of entinostat plus lapatinib was fairly well tolerated. The combination therapy suggests there was clinical activity in at-least 5 patients who had SD in this cohort of heavily pretreated trastuzumab-resistant MBC. Data from the EG104900 clinical trial showed that lapatinib plus trastuzumab significantly improved median overall survival compared with lapatinib alone. Therefore, this study was modified after 15 patients to add trastuzumab to the combination. We are currently conducting a phase 1b trial to determine the MTD of entinostat, trastuzumab and lapatinib. Citation Format: Jie Willey, Ricardo H Alvarez, Daniel J Booser, Sharon H Giordano, Ana M Gonzalez-Angulo, James L Murray, Vincente Valero, Jangsoon Lee, Naoto T Ueno, Summer A Jackson, Fahad A Faruqi. A phase I clinical trial of entinostat and lapatinib in patients with trastuzumab refractory HER2-positive metastatic breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-19-22.