Difficulty in recruiting patients

The purpose of this study is to evaluate the efficacy and safety of an adjuvant treatment of therapeutic cancer vaccine (AST-301, pNGVL3-hICD) in patients with HER2-low expression (IHC 1+ or 2+ and ISH-) and hormone receptor-negative(ER-, PR-) breast cancer with residual disease after neoadjuvant treatment.

Patients will be randomized 1:1 to either the Experimental arm (combination of AST-301/rhuGM CSF and standard adjuvant therapy) or the Control arm (combination of placebo/rhuGM CSF and standard adjuvant therapy). Standard adjuvant chemotherapy will be pembrolizumab or capecitabine.

Adjuvant therapy will be administered in compliance with the NCCN guideline for breast cancer (Version 8, 2021), and IP (AST-301) will be administered 3 times every 3 weeks in the adjuvant treatment period, with a booster administered at 24 weeks (±7 days) post the third dose of IP administration.

Survival follow up will be performed to determine invasive Disease Free survival(iDFS).

Not provided

Key Inclusion Criteria:

• Has a residual invasive cancer in the breast(non-pCR) after neoadjuvant treatment
• Has stage I, II, or III disease prior to surgery per American Joint Committee on Cancer (AJCC)
• HER 2 1+ by IHC or HER2 2+by IHC without gene amplification by ISH, as defined by American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines.
• Hormone receptor (ER and PR) negative by ASCO/CAP guidelines
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
• Demonstrates adequate organ function.

Key Exclusion Criteria:

• Has a history of hypersensitivity or other contraindications to rhGM-CSF
• Has a history of invasive malignancy ≤5 years prior to first administration of investigational drug except for adequately treated non-melanoma skin cancer or carcinoma in situ.
• Is on immune suppression therapy or has a history of immune suppression therapy ≤4 weeks prior to the first administration of investigational drugs
• Has a history of autoimmune disease or inflammatory disease
• Has active infection including tuberculosis, hepatitis B, hepatitis C or human immunodeficiency virus (HIV) infection
• Is pregnant or breastfeeding or expecting to conceive children