Nonsentinel lymph node metastases in cases of micrometastasis detected by sentinel lymph node biopsy after neoadjuvant chemotherapy

Background: There is a clinical need to omit axillary lymph node dissection (ALND) when residual disease in sentinel lymph nodes (SLNs) is low after neoadjuvant chemotherapy (NAC). This study aimed to clarify the relationship between micrometastasis in SLNs after NAC and additional non-SLN metastases by analyzing SLN biopsy results followed by ALND. Methods: This retrospective study reviewed clinical records of patients who underwent breast cancer surgery between January 2010 and June 2022 after NAC at Samsung Medical Center. Of 3944 patients, 806 underwent SLN biopsy followed by ALND. Intraoperative frozen SLN biopsy results were examined, including the number and size of metastases in SLNs, and further investigated the number of additional non-SLN metastases. Results: Among the 806 patients, 95 (11.8%) had micrometastasis on SLNs in frozen sections, of which 89 (93.7%) had clinically node-positive (cN1-3) breast cancer before NAC. Twenty-three patients (24.2%) exhibited positive additional non-SLNs after ALND. The presence of lymphovascular invasion (vs. absence; odds ratio [OR] = 4.02, p = .0151) and having two or more SLNs with micrometastasis (vs. a positive SLN; OR = 3.65, p = .0301) were significantly associated with additional non-SLN metastases. Tumor subtypes and breast pathological complete response after NAC showed no correlation with the additional non-SLN metastases. Conclusion: The study identified a 24.2% possibility of additional non-SLN metastasis if micrometastases was detected in the SLN after NAC. This rate is significant, indicating that ALND cannot be omitted if low volume residual disease, such as micrometastasis, is identified in the SLN after NAC.