The number of positive axillary lymph nodes (LNs) is the only node-related factor for prognostic evaluation of breast cancer recognized by AJCC (TNM staging). However, N staging may not completely reflect LN tumor involvement due to the erroneous count of LNs in the presence of matted LNs and different tumor volume in LNs. Additionally, the positive/total LN ratio (LNR) has been shown to outperform N staging in survival prediction. In our study, to better quantify the tumor involvement of axillary LNs, we measured the cross-sectional cancer area (CSCA) of the positive LNs in 292 breast cancer patients diagnosed between 1998 and 2000 in our institution and compared its prognostic value to that of number of positive LNs (metLN)/N stage and LNR. Statistical analyses of these three LN-related factors were performed by Kaplan-Meier method and multivariate Cox's regression model. Patients were divided into three groups based on the different LN CSCA (<50, 50–500, and >500？mm2), or LNR (<0.1, 0.1–0.65, and >0.65), or N stage (N1–N3). Multivariate analysis demonstrated LNR was the most significant LN-related survival predictor with hazard ratio (HR) 25.0 ( ), compared to the metLN (HR 0.09, ) and CSCA (HR 2.24, ). 1. Introduction Breast cancer was the most common malignancy in women in North America in 2010 [1]. The involvement of axillary LNs by cancer is one of the most important factors for cancer staging, treatment, and prognosis [2–5]. The surgical excision of the primary cancer and the axillary LN dissection has been considered as part of the standard management of invasive breast cancer [6–8]. Counting the number of positive axillary LNs was used for TNM staging [9], and it is the only node-related factor for the evaluation of breast cancer recognized by American Joint Committee on Cancer (AJCC) [10]. In general, evaluating 10 or more LNs is ideal for accurate assessment and the staging of breast cancer [6, 7]. Besides LN staging, other equally important prognostic factors associated with breast cancer are tumor size, histological grade, and hormone receptor status [11]. According to AJCC, based on the number of positive LNs (metLN), patients are divided into three N stages: N1 (1–3 positive LNs), N2 (4–9 positive LNs), and N3 (>9 positive LNs). There are some considerations of minimal tumor involvement such as isolated tumor cells (<0.2？mm or <200 tumor cells) and micrometastasis (>0.2？mm and/or >200 tumor cells and <2？mm) in N0 and N1, respectively [9]. However, the quantitative criteria have not been considered in the AJCC staging system in positive
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