ERBB2 and breast carcinoma: While efficacy data are well established, real-world safety data remain limited, particularly in Southeast Asian populations.<h4>Objective</h4>To assess the comprehensive toxicity profile of the 4AC-4THP regimen, including both cardiac and non-cardiac adverse events, in Vietnamese patients with HER2-positive early-stage breast cancer.<h4>Methods</h4>We conducted a retrospective multicenter study involving 52 women with stage II-III HER2-positive breast cancer treated with the 4AC-4THP neoadjuvant regimen at three oncology centers in Northern Vietnam between January 2020 and October 2024.