<h4>Background</h4>The aim of the study was to compare trastuzumab-based neoadjuvant therapy (NAT) with adjuvant therapy (AT) in a register-based cohort of Swedish patients with primary operable human epidermal growth factor receptor 2 (HER2)-positive breast cancer.<h4>Patients and methods</h4>The Swedish nationwide research database BCBaSe 3.0 was used to identify eligible patients with primary operable HER2-positive breast cancer treated with either NAT or AT between 2008 and 2019. The gene discussed is ERBB2; the disease is breast carcinoma.