Update on sentinel node pathology in breast cancer

Pathologic examination of the sentinel lymph nodes (SLNs) in patients with breast cancer has been impacted by the publication of practicing changing trials over the last decade. With evidence from the ACOSOG Z0011 trial to suggest that there is no significant benefit to axillary lymph node dissection (ALND) in early-stage breast cancer patients with up to 2 positive SLNs, the rate of ALND, and in turn, intraoperative evaluation of SLNs has significantly decreased. It is of limited clinical significance to pursue multiple levels and cytokeratin immunohistochemistry to detect occult small metastases, such as isolated tumor cells and micrometastases, in this setting. Patients treated with neoadjuvant therapy, who represent a population with more extensive disease and aggressive tumor biology, were not included in Z0011 and similar trials, and thus, the evidence cannot be extrapolated to them. Recent trials have supported the safety and accuracy of sentinel lymph node biopsy (SLNB) in these patients when clinically node negative at the time of surgery. ALND remains the standard of care for any amount of residual disease in the SLNs and intraoperative evaluation of SLNs is still of value for real time surgical decision making. Given the potential prognostic significance of residual small metastases in treated lymph nodes, as well as the decreased false negative rate with the use of cytokeratin immunohistochemistry (IHC), it may be reasonable to maintain a low threshold for the use of cytokeratin IHC in post-neoadjuvant cases. Further recommendations for patients treated with neoadjuvant therapy await outcomes data from ongoing clinical trials. This review will provide an evidence-based discussion of best practices in SLN evaluation.