Predictive Factors of Non-sentinel Lymph Node Involvement in Patients with Invasive Breast Cancer and Sentinel Node Micrometastases

Patient-related, tumor-related, and sentinel node (SN)-related factors have been identified with the aim of predicting non-SN status in patients with SN micrometastases. According to our previous experience, primary tumor size (p=0.005) and the presence of lymphovascular invasion (LVI) (p=0.000) significantly predicted non-SN status in patients with SN micrometastasis; moreover, non-SN metastases were never detected in patients with pT1a-1b, G1, and no LVI. A prospective assessment was undertaken in a validation set of 126 patients to confirm these findings. Univariate analysis indicated that primary tumor size (p=0.05), Scarff-Bloom-Richardson (SBR) grade (p=0.008), LVI (p=0.001), and the number of mitoses/mm2 (p=0.01) were significant predictors of non-SN status. By logistic regression analysis, tumor size (p=0.03), LVI (p=0.001), grade (p=0.003) and the number of mitoses/mm2 (p=0.01) were the only variables remaining in the model. Three subsets of patients were identified: i) 18.3% of patients (pT1, G1, and no LVI) had tumor-negative non-SN (no risk group); ii) 37.3% of patients (number of mitoses/mm2 <10, SBR grade II-III) had a rate of tumor-positive non-SN <15% (intermediate risk); iii) 44.4% of patients had a mean rate of non-SN involvement of 46% (high risk). By these parameters, more than 50% of patients could be selectively spared unnecessary axillary lymph node dissection without staging or therapeutic benefit, especially in patients with well-differentiated pT1 tumors without LVI.