Additional Study Information: NRG BR008 is a phase 3 study aims to compare the recurrence-free interval (RFI) among participants with early-stage, low-risk HER2+ breast cancer who undergo breast-conserving surgery and receive HER2-directed therapy and are randomized to not receive adjuvant breast radiotherapy (arm 2) versus those who are randomized to receive adjuvant radiotherapy per the current standard of care (arm 1). Participants will be stratified as follows: Age ( 60; 60), tumor size ( 1 cm; 1 cm), by pathologic(Adjuvant cohort) or clinical (Neoadjuvant cohort) staging, estrogen receptor status (positive; negative)and systemic therapy sequencing (Adjuvant or Neoadjuvant). Participants will then be randomized toArm 1 (Breast Radiation Therapy + Continuation of HER2-targeted therapy + HR therapy as per treatingphysician discretion) or Arm 2 (No Breast Radiation Therapy + Continuation of HER2-targeted therapy +HR therapy as per treating physician discretion). The standard total duration of HER2-targeted therapy is12 months. The primary objective of the study is to determine recurrence free interval for the two groups.Secondary objectives include 7-year cumulative incidence ipsilateral breast recurrence for radiationomitting arm, time to ipsilateral breast recurrence (IBR) by treatment arm, time to local regionalrecurrence (LRR) by treatment arm, determine disease-free survival by treatment arm, and overallsurvival.