This randomized phase III trial studies if not giving regional radiotherapy is just as good as using regional radiotherapy in keeping breast cancer from coming back in patients with estrogen receptor (ER) positive, HER2 negative node positive low risk breast cancer who have undergone breast conserving surgery or mastectomy. Women with ER positive breast cancer normally will receive endocrine therapy and some may receive chemotherapy to help prevent the cancer from coming back. Many women will also receive radiotherapy to the whole breast/chest area and the surrounding lymph glands (called regional radiotherapy). Radiation therapy uses high energy x-rays to kill tumor cells and shrink tumors. It is not known whether patients with low risk breast cancer need to receive regional radiotherapy. As a result, some women may be getting regional radiotherapy who do not need it and be exposed to the side effects of their treatment without benefit. This study will help to determine if regional radiotherapy can be omitted for low risk ER positive node positive breast cancer patients.