Therapeutic Cancer Vaccine (AST-301, pNGVL3-hICD) in Patients With Breast Cancer (Cornerstone001)

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).