Abstract P3-01-05: A feasibility study of sentinel lymph node detection and analysis of safety to omit axillary lymph node dissection in clinically node-negative breast cancer patients after neoadjuvant chemotherapy

Background: Concerns still remain about lower sentinel node (SN) detection and higher false-negative rates (FNR) in breast cancer patients treated with neoadjuvant chemotherapy (NAC), especially those who are clinically node-positive before NAC. It is necessary to analyze the validity of sentinel node biopsy (SNB) after NAC and evaluate whether the SN identification rate and FNR for clinically N0 (cN0) patients after NAC would be acceptable or not in order to omit axillary lymph node dissection (ALND). Objectives and methods: We identified SN by radioisotopic methods followed by completion of ALND in cN0 patients after NAC from 2013 to 2016 as part of a clinical research study (SNB group, N=68) to analyze the accuracy of SNB, and retrospectively investigated the prognosis of patients treated with NAC from 2006 to 2012 (control group, N=92) to evaluate whether the validity of SNB would be acceptable or not. Results: Mean patient ages in the SNB group and control group were 51.0 years and 49.5 years, respectively ( p =0.17), and the distribution of intrinsic subtypes was not significantly different between the two groups. The numbers of cN1≤ before NAC in the SNB group and control group were 85.5% (57/68) and 80.4% (74/92), respectively ( p =0.58), and the pathological complete response rates were 25.0% (17/68) and 19.6% (18/92), respectively ( p =0.41). Lymphoscintigraphy using 99m Tc-phytate acid was performed in the SNB group, and hot spots were detected at the ipsilateral axilla in 62 of 68 (91.2%) patients, in all of whom SNs could be identified by using a gamma-probe. The FNR, which indicates no metastasis in SNs and metastasis in non-SN, was 5.9% (4/68). Among these four patients, three were of the luminal type while one was triple negative. The number of patients without metastasis in both SN and non-SN, which are candidates for omission of ALND, was 26 of 68 (38.2%). They included eight of nine HER2-enriched patients and six of 13 luminal-HER2 patients. Conversely, there were no false-negative cases in these subtypes. Moreover, all SNs were identified even if there were metastases in SNs. Regarding the prognosis of the control group, the 10-year disease free survival of post-NAC N0 (ypN0) (52/92, 56.5%) and ypN1≤ (40/92, 43.5%) were 80.7% and 61.2%, respectively ( p =0.08); in addition, the 10-year overall survival of yN0 and ypN1≤ were 90.4% and 72.6% ( p =0.26). Thus, the prognosis of ypN1≤ was not significantly inferior to that of ypN0. If omission of ALND were performed for false negative cases, then the risk of axillary relapse would be a concern. However, these data indicate the possibility that 5.9% of FNR as shown in the SNB group would not have much influence on prognosis. Conclusion: The accuracy of SN detection by radioisotopic methods for cN0 breast cancer after NAC was not maintained like that for -early breast cancer although it was better than the results of previous studies. However, there were no false-negative cases in HER2-enriched and luminal-HER2 subtypes, which could be potential candidates for omission of ALND. In addition, omission of ALND for false-negative patients would have less influence on the prognosis. Citation Format: Maeno K, Yamamoto K, Ono M, Oba T, Iesato A, Ono K, Ito T, Kanai T, Ito K-I. A feasibility study of sentinel lymph node detection and analysis of safety to omit axillary lymph node dissection in clinically node-negative breast cancer patients after neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-01-05.