Grabenstetter A, Moo TA, Hajiyeva S, et al. - Sentinel lymph nodes (SLN) frozen section (FS) assessment in breast cancer patients treated with neoadjuvant chemotherapy (NAC) was evaluated for its FN rate and the histomorphologic factors associated with FN results. Researchers identified 711 patients who had FS SLN assessment; 522 negative, 181 positive, and 8 deferred. They observed the FN rate of 5.4% (28/522). Metastatic foci were identified in the majority (25/28, 89%) of FN cases exclusively on permanent sections, and these cases were not due to a true diagnostic interpretation error. FN cases were more frequently estrogen receptor-positive, progesterone receptor positive, human epidermal growth factor receptor-2 negative and histologic grade 1, which most likely reflects the lower rates of pathologic complete response in these tumors. Despite its limitations, FS seems to be a reliable modality to appraise the presence of SLN metastases in NAC treated patients.