Abstract P2-01-25: Not all sentinel lymph nodes are equal – A predictive model for axillary burden in early breast cancer

Introduction The Z11 trial demonstrates that an axillary lymph node dissection (ALND) can be avoided in patients with low axillary burden who undergo breast conserving surgery (BCS), combined with whole-breast radiotherapy and systemic therapy. Our group propose a standardisation of sentinel lymph node biopsy (SLNB), incorporating 2 novel sentinel nodal stations (SNS) which represent sequential echelons of SLN draining the breast – the intercostalbrachial nerve (ICB) and the medial pectoral neurovascular bundle (MP). By increasing the specificity and positive predictive value of SLNB, we aim to identify a subgroup of patients who undergo mastectomy who can be spared from ALND and its associated complications. Materials and Methods 313 female patients who underwent sentinel lymph node biopsy for breast cancer from 2 February 2012 to 19 December 2013 were prospectively studied. 12 patients had bilateral breast cancers, and each laterality was counted as distinct cases, giving a total of 325 cases. 7 had breast surgery performed prior to the SLNB, and the rest had their oncological surgery performed at the same setting of the SLNB. The surgeries were performed by three surgeons in the National Cancer Centre Singapore, using a specific surgical technique to identify SLN at the 2 SNS. Relevant patient demographics, status of SNS and the rates of metastatic non-sentinel lymph nodes were collected and analysed. Results A total of 325 SLNBs using the ICB and MP SNS were identified from 169 simple mastectomies, 35 skin sparing mastectomies, and 129 breast conserving surgeries. The median age was 56 (range 27-89). The ICB SLN and MP SLN were identified in 313 (96.3%) and 258 (79.4%) cases respectively. In 249 (76.6%) cases were both ICB and MP nodes identified, of which 55 (16.9%) had metastatic involvement of the SLN. An axillary clearance was performed if at least one ICB or MP node was positive, and only 27 (49.1%) had further axillary involvement. More than 2 positive SLNs had 100% positive predictive value for further axillary LN metastases. There was a low sensitivity (29.6%) and high false negative rate (70.4%) for positive axillary nodes in patients with ≤2 positive SLNs. MP nodal status, however, was 85.7% specific (p p =0.649) and a positive predictive value of 76.5% for axillary nodal involvement. Logistic regression also shows that MP node status is significant for predicting axillary nodal status (OR 5.57, p =0.006). Conclusion Our study shows that MP node status is specific, and has a positive predictive value for further axillary LN metastases. Therefore, we propose that in all patients who undergo SLNB with their BCS or mastectomy, an axillary clearance should be performed if the MP node is positive, regardless of the number of positive SLNs. Citation Format: Yirong Sim, Sue Zann Lim, Shaun S Tan, Alvona Z Loh, Cindy Lim, Preetha Madhukumar, Gay H Ho, Veronique KM Tan, Kong Wee Ong. Not all sentinel lymph nodes are equal – A predictive model for axillary burden in early breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P2-01-25.