We evaluated SLNB positivity rates and treatment characteristics among patients undergoing BCT versus mastectomy.<h4>Methods</h4>Patients with cT1N0M0 HR+/HER2- unifocal invasive ductal carcinoma with negative axillary ultrasound undergoing upfront BCT + radiation therapy (RT) or mastectomy +/- RT were included (2010-2023). The gene discussed is ERBB2; the disease is invasive ductal breast carcinoma.