Is Low-Volume Disease in the Sentinel Node After Neoadjuvant Chemotherapy an Indication for Axillary Dissection?

Intraoperative evaluation of sentinel lymph nodes (SLNs) after neoadjuvant chemotherapy (NAC) has a higher false-negative rate than in the primary surgical setting, particularly for small tumor deposits. Additional tumor burden seen with isolated tumor cells (ITCs) and micrometastases following primary surgery is low; however, it is unknown whether the same is true after NAC. We examined the false-negative rate of intraoperative frozen section (FS) after NAC, and the association between SLN metastasis size and residual disease at axillary lymph node dissection (ALND). Patients undergoing SLN biopsy after NAC were identified. The association between SLN metastasis size and residual axillary disease was examined. From July 2008 to July 2017, 702 patients (711 cancers) had SLN biopsy after NAC. On FS, 181 had metastases, 530 were negative; 33 negative cases were positive on final pathology (false-negative rate 6.2%). Among patients with a positive FS, 3 (2%) had ITCs and no further disease on ALND; 41 (23%) had micrometastases and 125 (69%) had macrometastases. Fifty-nine percent of patients with micrometastases and 63% with macrometastases had one or more additional positive nodes at ALND. Among those with a false-negative result, 10 (30%) had ITCs, 15 (46%) had micrometastases, and 8 (24%) had macrometastases; 17 had ALND and 59% had one or more additional positive lymph nodes. Overall, 1/6 (17%) patients with ITCs and 28/44 (64%) patients with micrometastases had additional nodal metastases at ALND. Low-volume SLN disease after NAC is not an indicator of a low risk of additional positive axillary nodes and remains an indication for ALND, even when not detected on intraoperative FS.