A Study of A166 in Patients With HER2-Positive Unresectable or Metastatic Breast Cancer

Phase 2 Study of A166 in HER2-positive Metastatic Breast Cancer Patients Who Were Previously Treated With TOP1-ADCs

Evaluation of the efficacy of A166 in Patients with HER2-Positive unresectable or metastatic breast cancer previously treated with TOP1 inhibitor Antibody-Drug Conjugates

Study Overview

• Status: Recruiting
• Conditions: Her 2 Positive Breast Cancer
• Intervention / Treatment: Drug: A166

Detailed Description

This study will evaluate the efficacy of A166 in patients with HER2-positive unresectable or metastatic breast cancer previously treated with TOP1 inhibitor Antibody-Drug Conjugates.

A166 will be administered every 3 weeks (Q3W) intravenous (IV) infusion.

• Study Type: Interventional
• Enrollment (Estimated): 40
• Phase: Phase 2

Contacts and Locations

• Study Contact: Name: Min Yan, Professor; Phone Number: 0371-65588404; Email: ym200678@126.com

Study Locations

• China
  • Henan
    • Zhenzhou, Henan, China, 450000
      • Recruiting
      • Henan Provincial Cancer Hospital
      • Contact: Min Yan, Professor; Phone Number: 037165588404; Email: ym200678@126.com

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

1. Male or female patient ≥ 18 years and ≤ 75 years when signing the informed consent form.
2. Breast cancer patients by histopathology and/or cytology documented.
3. In the advanced or metastatic stage, having received no more than 5 lines of systemic therapy, one of which must include a HER2 ADC with a topoisomerase inhibitor payload.
4. Patients must have experienced disease progression or intolerance during or after the most recent treatment prior to randomization.
5. At least one measurable lesion according to RECIST 1.1 criteria.

Exclusion Criteria:

1. Previous treatment with A166 or any HER2-targeted antibody-drug conjugate (ADC) with a microtubule inhibitor payload.
2. Known history of severe hypersensitivity to other monoclonal antibodies, or allergy to A166 or their components.
3. Permanent discontinuation of trastuzumab or its biosimilars due to any toxicity in prior treatments.
4. Presence of severe corneal epithelial disease at baseline; or inability to perform daily activities without contact lenses.
5. Presence of spinal cord compression or clinically active central nervous system (CNS) metastases.
6. Other conditions considered by the investigator to make the patient unsuitable for participation in the study.

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: A166; A166 is administered intravenously at a dose of 4.8 mg/kg every 21 (±3) days (q3w).	Drug: A166; intravenous(IV) infusion (Q3W)

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Objective response rate(ORR)	ORR is defined as the percentage of patients who achieve complete response(CR) or partial response (PR), as assessed by investigator per RECIST 1.1	Within 24 months of last patient enrolled

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Progression-free survival (PFS)	PFS, 6-month PFS, 12-month PFS.PFS as assessed by investigator according to RECIST v 1.1	Within 24 months of last patient enrolled
Overall survival (OS)	OS, 1-year survival rate, 1.5-year survival rate, and 2-year survival rate.OS defined as time from inclusion until death	Within 48 months of last patient enrolled
Disease control rate(DCR)	DCR is defined as the percentage of patients who achieve CR, PR or stable disease (SD), as assessed by investigator per RECIST 1.1	Within 24 months of last patient enrolled
Duration of response(DOR)	DoR is defined as the time from the date of first documented CR or PR until date of documented disease progression per RECIST 1.1, as assessed by investigator or death due to any cause, whichever occurs first.	Within 24 months of last patient enrolled
Clinical Benefit Rate (CBR)	CBR is defined as a patient having a best overall response of a complete response (CR), partial response (PR), or stable disease for at least 6 months.	Within 24 months of last patient enrolled

Collaborators and Investigators

• Sponsor: Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd.

Study record dates

Study Major Dates

• Study Start (Actual): September 20, 2024
• Primary Completion (Estimated): September 20, 2027
• Study Completion (Estimated): December 31, 2027

Study Registration Dates

• First Submitted: December 3, 2025
• First Submitted That Met QC Criteria: December 17, 2025
• First Posted (Actual): December 23, 2025

Study Record Updates

• Last Update Posted (Actual): May 8, 2026
• Last Update Submitted That Met QC Criteria: May 5, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Other Study ID Numbers: KL166-II-08

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