Tailored radiation may spare breast cancer patients from arm swelling

This study is testing whether giving radiation therapy tailored to each patient's risk level can reduce arm swelling (lymphedema) while still controlling cancer in women with early-stage breast cancer that has spread to a sentinel lymph node. Participants receive either whole breast radiation alone or radiation to the breast plus regional lymph nodes, depending on clinical and genomic risk assessments. The goal is to see if a personalized approach can avoid the need for more extensive surgery and minimize side effects without increasing the chance of cancer returning.