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

An Open-Label, Single-Center, Exploratory Phase Ib/II Clinical Study of Entinostat Combined With Pyrotinib Plus Endocrine Therapy in Patients With Advanced Triple-Positive Breast Cancer After Trastuzumab Failure

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.

Study Overview

• Status: Recruiting
• Conditions: Breast Cancer; Metastatic Breast Cancer; HER2-positive Breast Cancer; Hormone Receptor-Positive Breast Cancer
• Intervention / Treatment: Drug: entinostat; Drug: Pyrotinib; Drug: endocrine therapy

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Estimated): 94
• Phase: Phase 2; Phase 1

Contacts and Locations

• Study Contact: Name: Yehui Shi, MD, PhD; Phone Number: +86 18622221183; Email: shiyehui@tjmuch.com

Study Locations

• China
  • Tianjin Municipality
    • Tianjin, Tianjin Municipality, China, 300060
      • Recruiting
      • Tianjin Medical University Cancer Institute and Hospital
      • Contact: Yehui Shi, MD PhD; Phone Number: +86 23340123; Email: ec_tjcih@126.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

1. Age ≥ 18 and ≤ 75 years, female, premenopausal or postmenopausal.
2. Histologically confirmed HR+/HER2+ breast cancer (HER2 positive defined as IHC 3+ or FISH confirmed by the pathology department of the study center).
3. Histologically confirmed locally advanced breast cancer (not amenable to curative local therapy) or recurrent/metastatic breast cancer.
4. Prior treatment with trastuzumab and taxane-based anticancer therapy.
5. Received 1-2 prior lines of systemic anticancer therapy in the advanced setting.
6. Life expectancy ≥ 3 months.
7. At least one measurable lesion per RECIST v1.1.
8. ECOG performance status 0-2.
9. All acute toxicities from prior anticancer therapy resolved to Grade 0-1 (per NCI CTCAE v5.0), except alopecia and toxicities deemed by the investigator to pose no safety risk.
10. Adequate bone marrow function: ANC ≥ 1.5×10^9/L, platelet ≥ 100×10^9/L, hemoglobin ≥ 90 g/L.
11. Adequate hepatic and renal function: TBIL ≤ 1.5×ULN; ALT and AST ≤ 2.5×ULN (or ≤ 5×ULN in the presence of liver metastases); BUN and Cr ≤ 1.5×ULN with creatinine clearance ≥ 50 mL/min.
12. Voluntarily participate and sign written informed consent. -

Exclusion Criteria:

1. Factors significantly affecting oral drug absorption, such as inability to swallow, chronic diarrhea, or intestinal obstruction.
2. Prior treatment with any HDAC inhibitor for antitumor therapy.
3. Prior or current use of any HER2-targeted tyrosine kinase inhibitor (including lapatinib, neratinib, pyrotinib, etc.).
4. Known allergy to any component of the study drugs.
5. Other malignancy within 5 years prior to enrollment, except cured papillary thyroid carcinoma, cervical carcinoma in situ, basal cell carcinoma, or squamous cell carcinoma of the skin.
6. Participation in another drug clinical trial within 4 weeks prior to enrollment.
7. History of immunodeficiency, including HIV positivity, other acquired or congenital immunodeficiency diseases, or history of organ transplantation.
8. Uncontrolled significant cardiovascular disease: clinically significant QTc interval prolongation or QTc > 450 ms at screening; severe cardiac impairment (NYHA > Class II); unstable angina or myocardial infarction within 6 months; or severe arrhythmia.
9. Pregnant or lactating women, or positive pregnancy test at baseline; or women of childbearing potential who are unwilling to use effective contraception during the study and for at least 8 weeks after the last dose.
10. Concomitant diseases that, in the investigator's judgment, could seriously endanger patient safety or affect study completion (e.g., severe hypertension, diabetes, thyroid disease, active infection).
11. Known history of neurological or psychiatric disorders, including epilepsy or dementia.
12. Active hepatitis (HBV: HBsAg positive with HBV DNA ≥ 500 IU/mL; HCV: HCV antibody positive with HCV RNA > ULN).

13. Any condition that, in the investigator's judgment, makes the patient unsuitable for study participation.

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Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm

Intervention / Treatment

Experimental: Entinostat + Pyrotinib + Endocrine Therapy; Participants receive entinostat (weekly, oral), pyrotinib (400 mg daily, oral), and physician-selected endocrine therapy (tamoxifen, aromatase inhibitor, or fulvestrant; plus OFS for premenopausal patients) in 28-day cycles. Part Ib: dose-escalation of entinostat (3 mg, 4 mg, 5 mg) following the 3+3 design to determine MTD/RP2D. Part II: expansion at RP2D to evaluate efficacy and safety.

Drug: entinostat; Entinostat is an oral, selective class I histone deacetylase (HDAC) inhibitor, administered at 3 mg, 4 mg, or 5 mg once weekly on Days 1, 8, 15, and 22 of each 28-day cycle, taken 60 minutes after a meal. The dose is determined by the 3+3 dose-escalation design in Part Ib.; Drug: Pyrotinib; Pyrotinib is an oral, irreversible pan-ErbB receptor tyrosine kinase inhibitor, administered at a fixed dose of 400 mg once daily, taken 30 minutes after a meal, in each 28-day cycle.; Drug: endocrine therapy; Physician-selected endocrine therapy based on patient's prior treatment history and menopausal status. Options include tamoxifen (20 mg daily), aromatase inhibitors (letrozole 2.5 mg daily, anastrozole 1 mg daily, or exemestane 25 mg daily), or fulvestrant (500 mg intramuscularly on Days 1, 15, 29, and once monthly thereafter). For premenopausal patients, ovarian function suppression (OFS) with GnRH agonists is added. All endocrine agents are administered according to their approved package inserts.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Dose-Limiting Toxicity (DLT), Maximum Tolerated Dose (MTD), and Recommended Phase II Dose (RP2D) of Entinostat in Combination with Pyrotinib and Endocrine Therapy	DLT is assessed during the first 28-day cycle. MTD and RP2D are determined based on the 3+3 dose-escalation design.	Cycle 1 (Day 1 to Day 28)
Progression-Free Survival (PFS)	PFS is defined as the time from the first dose of study treatment to the first documented disease progression per RECIST v1.1 or death from any cause, whichever occurs first.	From first dose to disease progression or death, assessed up to 36 months
Incidence and Severity of Adverse Events (AEs) and Serious Adverse Events (SAEs)	AEs and SAEs are graded according to NCI CTCAE v5.0, including hematological and non-hematological toxicities.	From signing of informed consent through 28 days after the last dose of study treatment

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Objective Response Rate (ORR)	ORR is defined as the proportion of participants with a best overall response of complete response (CR) or partial response (PR) based on RECIST v1.1.	From first dose to disease progression, assessed up to 36 months
Disease Control Rate (DCR)	DCR is defined as the proportion of participants with a best overall response of CR, PR, or stable disease (SD) based on RECIST v1.1.	From first dose to disease progression, assessed up to 36 months
Clinical Benefit Rate (CBR)	CBR is defined as the proportion of participants with a best overall response of CR, PR, or SD lasting for at least 6 months based on RECIST v1.1.	From first dose to disease progression, assessed up to 36 months
Duration of Response (DoR)	DoR is defined as the time from the first documented CR or PR to the first documented disease progression per RECIST v1.1 or death from any cause.	From first documented response to disease progression or death, assessed up to 36 months
Overall Survival (OS)	OS is defined as the time from the first dose of study treatment to death from any cause.	From first dose to death from any cause, assessed up to 36 months
Patient-Reported Outcomes (PRO) - EORTC QLQ-C30	Health-related quality of life assessed using the EORTC QLQ-C30 (Version 3.0) Chinese version. The questionnaire includes functional scales, symptom scales, and global health status/QoL.	Baseline, every 2 cycles during treatment, and at end of treatment, assessed up to 36 months

Collaborators and Investigators

• Sponsor: Tianjin Medical University Cancer Institute and Hospital
• Collaborators: Taizhou EOC Pharma Co., Ltd.

Study record dates

Study Major Dates

• Study Start (Actual): June 23, 2025
• Primary Completion (Estimated): February 1, 2027
• Study Completion (Estimated): February 1, 2027

Study Registration Dates

• First Submitted: July 12, 2026
• First Submitted That Met QC Criteria: July 12, 2026
• First Posted (Actual): July 16, 2026

Study Record Updates

• Last Update Posted (Actual): July 16, 2026
• Last Update Submitted That Met QC Criteria: July 12, 2026
• Last Verified: July 1, 2026

More Information

Terms related to this study

• Keywords: HER2-positive; Endocrine Therapy; Entinostat; Pyrotinib; HDAC Inhibitor; Hormone Receptor-positive; Epigenetic Therapy; Trastuzumab Resistance; Triple-positive Breast Cancer
• Additional Relevant MeSH Terms: Neoplasms by Site; Neoplasms; Skin Diseases; Breast Diseases; Skin and Connective Tissue Diseases; Breast Neoplasms; pyrotinib; entinostat
• Other Study ID Numbers: CSIIT-C54

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No