Abstract P6-08-52: Predicting the likelihood of additional non sentinel lymph node metastasis in early breast cancer: Novel sentinel nodal station status versus Singapore General Hospital nomogram

Background: Sentinel lymph node biopsy (SLNB) has been widely used in early breast cancer patients for the detection of axillary nodal metastasis. We were the first to describe 2 novel sentinel nodal stations (SNS) in relation to the intercostobrachial nerve (ICB) and the medial pectoral neurovascular bundle (MP) at which sentinel lymph nodes (SLN) were consistently identified, even only with the use of blue dye. In a pilot study involving 176 cases, we have shown that the ICB and MP SNS represent sequential echelons of SLN draining the breast. It was observed that the status of the MP SNS can be used in predicting the likelihood of additional non sentinel lymph node metastasis in early breast cancer. Thus, we aim to compare this against the Singapore General Hospital (SGH) nomogram, the existing standard predictive model in the local population. The SGH nomogram was developed from predictors in the Memorial Sloan-Kettering Cancer Centre (MSKCC) nomogram. It uses only 3 pathological parameters: lymphovascular invasion, number of positive and negative SLN. This has been shown to be at least equal if not better than the MSKCC nomogram as a predictive model in the Singapore population. Methods : All patients who underwent oncologic breast surgery and SLNB (using the SNS identification technique) at the Department of Surgical Oncology, National Cancer Centre Singapore from February 2012 to December 2013 inclusive were reviewed. Patients who fulfilled the following selection criteria were included in the study: [1] invasive ductal or lobular carcinoma, [2] SLN identified in both ICB and MP SNS,[3] axillary clearance done with total lymph nodes ≥ 10, based on a positive SLNB. The performance of the MP SNS status and SGH nomogram in predicting the likelihood of additional non sentinel lymph node metastasis was compared with the calculation of the area under the receiver-operating characteristic curve (AUC). Results: A total of 49 patients were identified. Majority of the patients had early breast cancers: 94% had tumour size ≤5cm and 71% had N1 disease. The median number of total SLN, ICB and MP nodes identified were 3 (range 2-14), 2 (range 1-7) and 1 (range 1-12) respectively. The median number of positive and negative SLN were both 1 (range 1-5 and 0-9 respectively). The positive predictive value of MP SNS status for additional non sentinel lymph node metastasis was 76.5% (95% CI: 50.1-93.2). The strong association was proven by an odds ratio of 7.15 (95% CI 1.86-27.50, p-value: 0.002). The negative predictive value of MP SNS for eventual N stage was 93.8% (95% CI: 79.2-99.2). In most of the cases, the nodal stage remained at N1 in the presence of negative MP node. The model with MP SNS status yielded an AUC of 0.706 (95% CI: 0.579-0.832) which was higher than that of the SGH nomogram, 0.658 (95% CI: 0.503-0.813). Conclusions: The novel MP SNS proved to be a single parameter which predicts the likelihood of additional non sentinel lymph nodes metastasis better than the SGH nomogram. More importantly, from the clinical point of view, the MP SNS status can be made available intra-operatively and hence guide the decision for further axillary dissection. Citation Format: Sue Zann Lim, Puay Hoon Tan, Gay Hui Ho, Preetha Madhukumar, Yirong Sim, Shaun Shi Yan Tan, Cindy Lim, Veronique Kiak Mien Tan, Kong Wee Ong. Predicting the likelihood of additional non sentinel lymph node metastasis in early breast cancer: Novel sentinel nodal station status versus Singapore General Hospital nomogram [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 P6-08-52.