This study is looking at breast cancer treatment to see if some women need less radiation. Breast cancer is a disease where cells in the breast grow out of control. Some women with *low-risk breast cancer* (cancer that is not likely to spread) might be getting extra radiation that they don't need, which can have side effects. The study compares usual care with radiation to no radiation. To join, women must have a specific type of breast cancer and be over 35 years old. They must also be receiving certain therapies like endocrine therapy, which are medications that lower estrogen to stop cancer growth, or chemotherapy, which uses strong medicine to kill cancer cells.

• The study requires regular follow-ups to ensure proper documentation of treatment effects.
• Patients must consent to provide tissue and blood samples for research.
• Women of childbearing age must agree to use effective birth control during the study.