Entinostat Plus Pyrotinib and Endocrine Therapy in Advanced Triple-Positive Breast Cancer After Trastuzumab Failure

Overview

This is an open-label, single-center, exploratory, Phase Ib/II clinical trial evaluating the safety and efficacy of entinostat combined with pyrotinib and endocrine therapy in patients with advanced hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-positive (HER2+) breast cancer who have failed prior trastuzumab-based therapy. The study consists of two parts: Part I (Phase Ib) employs a 3+3 dose-escalation design to determine the dose-limiting toxicity (DLT), maximum tolerated dose (MTD), and recommended Phase II dose (RP2D) of entinostat when given in combination with pyrotinib (400 mg daily) and endocrine therapy. Part II (Phase II) uses a Simon two-stage design to further evaluate the efficacy and safety of the combination at the RP2D. The primary efficacy endpoint is progression-free survival (PFS) based on RECIST v1.1. A total of approximately 79-94 participants will be enrolled.

Background: Triple-positive breast cancer (TPBC), characterized by co-expression of HR and HER2, accounts for approximately 10% of all breast cancer cases. Despite the availability of anti-HER2 targeted therapies, patients with TPBC often have suboptimal responses to chemotherapy-containing regimens, and endocrine therapy resistance remains a clinical challenge. Histone deacetylase (HDAC) inhibitors have shown synergistic effects with HER2-targeted agents and endocrine therapy through epigenetic modulation, potentially reversing drug resistance and enhancing anti-tumor immunity. Objective: To explore the DLT, MTD, and RP2D of entinostat in combination with pyrotinib and endocrine therapy, and to preliminarily evaluate the safety and efficacy of this regimen in HR+/HER2+ advanced breast cancer patients who have failed trastuzumab therapy. Study Design: This is a two-part study. Part I (Phase Ib) is a single-arm, open-label, dose-escalation trial following the traditional 3+3 design. Entinostat is administered at escalating doses (3 mg, 4 mg, and 5 mg) once weekly, in combination with a fixed dose of pyrotinib (400 mg daily) and physician-selected endocrine therapy, in 28-day cycles. The DLT observation period is the first cycle. Part II (Phase II) is a single-arm, two-stage (Simon's optimal design) trial. Participants will receive entinostat at the MTD/RP2D established in Part I, combined with pyrotinib (400 mg daily) and endocrine therapy. A total of 76 evaluable participants are planned for Part II, with an interim analysis after the first 24 participants. The study is expected to enroll approximately 79-94 participants over 24 months, with an additional 12 months of follow-up. Key Eligibility: Female patients aged 18-75 years with histologically confirmed HR+/HER2+ locally advanced or metastatic breast cancer, who have received prior trastuzumab and taxane therapy, with 1-2 prior lines of systemic therapy in the advanced setting, ECOG PS 0-2, and measurable disease per RECIST v1.1. Statistical Methods: PFS will be estimated using the Kaplan-Meier method. ORR, DCR, CBR, DoR, and PRO will be summarized with descriptive statistics and 95% confidence intervals. Safety data will be tabulated by type, severity, and relationship to study drugs.