What guides regional nodal irradiation in node positive breast cancer following upfront sentinel lymph node biopsy?

BACKGROUND: This study aimed to evaluate decision-making patterns among international experts regarding breast cancer regional node irradiation (RNI), using an objective, consensus-driven approach. METHODS: Twenty-one international radiation oncology experts were invited to participate in a consensus-based evaluation of RNI recommendations. Participants provided responses to clinical scenarios involving early-stage breast (cN0) cancer with sentinel lymph node biopsy (SNLB)-positive findings (pN1a) without completion axillary lymph node dissection (ALND). Decision-making parameters, including patient age, tumour characteristics, and biological risk factors were analysed. FINDINGS: Of the 21 experts, 19 completed the evaluation. Responses included 22 different decision-making criteria and demonstrated considerable variability in decision-making, even after simplifying treatment options. Consensus was most frequently observed in high- and low-risk cases, with comprehensive RNI or omission of RNI being recommended, respectively. However, for intermediate-risk scenarios, no clear agreement was reached reflecting different clinical considerations and assessment of risk factors. INTERPRETATION: Due to many randomised studies investigating different risk factors that do not always coincide, breast cancer experts rely on a wide variety of criteria to recommend RNI for pN1(sn) breast cancer, leading to heterogeneity in decision-making. With this work we aim to raise awareness of this challenge to provoke revision of current guidelines and expert-based recommendations.