ESTRO 2021 Abstract Book

S908

ESTRO 2021

cancer (BC) following positive sentinel node biopsy (SLNB) and to investigate the association with risk factors. Nodal distribution along the 3 axillary levels was evaluated in order to suggest the extension of radiotherapy (RT) fields according to risk factors. Materials and Methods Clinical BC stages T1-T3, N0-3 undergoing NAST from 2001 to 2018 were identified from an institutional database. After NAST, all of them presented clinically negative axilla and SLNB was planned. Due to the intraoperative finding of metastatic SLNB, They underwent completion axillary lymph-nodes dissection (AxLND). Risk factors which can play as predictors of metastatic non-SLNs were identified, using both multivariate (MV) logistic regression and linear regression models. Accuracy of MV model was evaluated by the area under receiver operating characteristics curve (ROC AUC). The distribution of non-SLNs in the 3 levels of the axilla was observed. Results Two hundred and sixty-five women were included in the analysis. Patients, tumour, and treatment characteristics are described in Table 1. Positive non-SLNs were found in 62.3% of cases. At MV, statistically significant variables were older age (p 0.0473), clinically positive nodes (p 0.0052), SLN extracapsular extension (ECE, p <0.0001), and higher ratio of positive SLNs/total SLNs (p 0.0002). The ROC AUC was 0.6990 ( Figure 1 ). ECE and higher ratio of positive SLNs/total SLNs were independent predictive factors of III axillary level positivity.

Table 1. Baseline characteristics of the study population