Implication of Extracapsular Invasion of Sentinel Lymph Nodes in Breast Cancer: Prediction of Nonsentinel Lymph Node Metastasis

Accurate intraoperative diagnosis of sentinel lymph node (SLN) metastases enables the selection of patients who require axillary lymph node dissection (ALND). However, many patients with positive SLN do not show metastasis to other axillary lymph nodes. In this study, we investigated the factors that may determine the likelihood of additional positive nodes in the axilla when metastasis is found in the SLN. SLN biopsy was performed on 276 patients with breast cancer with clinically negative nodes, of which 46 (16.6%) had positive SLNs and underwent ALND. Eleven (23.9%) of these 46 cases had additional metastasis in nonsentinel lymph nodes (NSLN). The clinical and pathological features of these cases were reviewed and statistical analysis was performed. All cases of positive nodes in NSLN in our series had extracapsular invasion (ECI) at the metastatic SLNs. Furthermore, the absence of ECI of SLN was significantly associated with the absence of metastasis in the NSLN (P < 0.001). As contributing factors, the absence of lymphatic invasion at the primary tumor, primary tumor size (< 2 cm) and foci size in the metastatic SLN fell short of reaching statistical significance. Other factors, including histological type, pathological grade, estrogen receptor status, HER2 status, and age, were not significantly associated with metastatic involvement of NSLN. Our results suggest that the presence of ECI at metastatic SLNs is a strong predictor for residual disease in the axilla. These findings imply the possibility that ALND might be foregone in the treatment of patients with breast cancer without ECI at metastatic SLNs.