A Decision Tree To Predict Four or More Positive Axillary Lymph Nodes in Breast Cancer Patients with Positive Sentinel Node Biopsy: Determining Necessity for Regional Nodal Irradiation in the Absence of Axillary Dissection.

Abstract

Abstract Background: Regional Nodal Irradiation (RNI) is indicated for breast cancer patients with ≥4 positive axillary lymph nodes (ALN). The need for RNI is unclear for women who don't undergo axillary lymph node dissection (ALND) yet have 1-3 positive sentinel lymph nodes (SLN). In an effort to guide clinician decision-making and potentially spare patients combined toxicities of ALND and radiation, the purpose of this study was to create a decision tree of clinicopathologic variable interactions to predict patients with ≥4 positive ALN.Methods: We reviewed the records of 197 women with breast tumors <5cm and 1-3 positive SLN. After ALND, patients were labeled as having < 4 or ≥ 4 positive ALN. Ten clinicopathologic predictive variables were identified for analysis: patient age, size of tumor, histological type, tumor grade, number of metastatic SLN, largest SLN metastasis size, detection method, estrogen receptor, Ki67 and lymphovascular invasion (LVI). The analysis used Chi-Square Automatic Interaction Detection (CHAID SPSS), a non-parametric, stepwise “regression tree” analysis, with Bonferroni adjusted p-values to create a decision tree.Results: 141 patients had < 4 and 56 had ≥ 4 positive ALN. Three variables were selected into the CHAID tree: LVI, the number of metastatic SLNs, and largest SLN metastasis size. 100% of patients (N=42) had < 4 positive ALN if negative for LVI and had only 1 positive SLN with a metastasis size < 0.2cm (p-value < 0.0432). For patients with LVI (N=77), 13 of 14 (93%) had < 4 positive ALN if the SLN metastasis size was < 0.2cm (p < .0014). The highest prevalence of ≥ 4 positive ALN were patients with LVI and a SLN metastasis size > 0.2cm.Conclusion: The CHAID analysis more accurately predicted patients with < 4 positive ALN compared to those with ≥4. The decision tree provides a new tool for the clinician to determine the necessity for RNI without ALND. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1026.