This study is for patients with early-stage HER2-positive breast cancer. HER2 is a protein that can affect the growth of cancer cells. The study examines if patients can skip radiation therapy after breast-conserving surgery when they take HER2-targeted therapy. HER2-targeted therapy includes drugs designed to fight cancer cells with the HER2 protein. Radiation therapy uses high-energy rays to kill cancer cells.

The aim is to see if it's safe to skip radiation without increasing the risk of cancer returning. This could mean fewer side effects, less time in treatment, and lower costs for patients. The study will compare groups of patients who receive radiation therapy with those who do not.

• The study lasts several years to track cancer recurrence.
• Participants must be 40 or older and have had specific treatments with HER2-targeted therapy and surgery.
• Patients get regular check-ups and follow-up care during the study.

Eligible patients include those who have had breast-conserving surgery and completed certain chemotherapy and HER2 therapy. This study does not include patients with large tumors, certain other cancers, or those who've had radiation before.