Abstract ES6-1: Sentinel Node Biopsy in Breast Cancer: Before or after Neoadjuvant Chemotherapy?
Authors: Mamounas EP 
Published: August 2014

Neoadjuvant chemotherapy (NC) was originally used to render inoperable breast cancer (BC) patients to operable candidates. Its use subsequently expanded to operable BC patients requiring mastectomy to convert them to candidates for breast conserving surgery. NC has also been shown to downstage axillary lymph nodes in up to 40–50% of patients. This observation, coupled with the development and validation of sentinel node biopsy (SNB) in patients with operable BC provided yet another potential advantage for the use of neoadjuvant over adjuvant chemotherapy, i.e. the potential to decrease the extent and morbidity of axillary surgery.

Several small, single-institution studies have examined the efficacy of lymphatic mapping and the accuracy of SNB after NC with significant variability in the rate of SN identification and in the rate of false negative SN. Nonetheless, when these studies are examined collectively or when larger, multi-center data sets are analyzed, SNB after NC appears to have somewha lower rate of SN identification but similar rate of false negative SN compared to SNB before systemic therapy. This also appears to be the case even in patients who have documented involvement of the axillary nodes before NC. Results of two prospective studies on this subject (ACOSOG 1071 and SENTINA) will be presented at the 2012 SABCS.

Some have proposed that candidates for NC should have SNB performed before NC rather than after. They argue that this approach obtains information on the status of the SN without the potential confounding effects of NC and SN negative patients can avoid axillary dissection. Although this approach may be useful in patients who will not need adjuvant/neoadjuvant chemotherapy if the SN is negative, it is not generally useful for the majority of candidates for NC. SNB before NC commits patients to two surgical procedures whether the SN is negative or positive and this approach does not take advantage of the down-staging effect of NC on the axillary nodes.

Knowledge of the pathologic SN status before NC does not seem to help in deciding which NC regimen to use or whether to use additional adjuvant chemotherapy after surgery. Furthermore, the prognostic significance of negative axillary nodes after NC and prior positive SNB is dubious since node negativity in this setting may reflect axillary nodal down-staging or just the prior removal of all positive nodes by SNB. Lastly, it has been argued that knowing whether the axillary nodes are involved before NC may provide useful information regarding the need for postoperative XRT to regional lymph nodes or the chest wall (after mastectomy). Recent results on the rates and patterns of loco-regional recurrence (LRR) from two NSABP NC trials (B-18 and B-27) have shown that achievement of pathologic complete response (pCR) in the breast with histologically negative axillary nodes at surgery is an independent predictor of LRR and that LRR rates are low for patients who are clinically node positive before NC but histologically node-negative after NC, particularly if they have pCR in the breast. Thus, based on this data the value of knowing the pathologic status of the SN(s) before NC is further diminished.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr ES6-1.