The predictive value of micrometastasis in nonsentinel lymph nodes

The rate of micrometastatic disease (MMD) to nonsentinel lymph nodes (NSLNs) has been shown to vary considerably in the literature. We identified patients with breast cancer with MMD (N1mi) and measured the incidence of NSLN involvement. We then compared these patients with those who had no metastasis to the SLN (N0) and those who had macrometastasis to the SLN (N2) in an attempt to better understand the behavior of patients with N1mi positivity. A retrospective analysis was conducted on 574 patients with invasive breast cancer between January 2000 and December 2007. Patients were stratified into three groups: no metastasis (N0), MMD (N1mi), and macrometastasis (N2). Chi square analysis and logistic regression models using SPSS software were applied to determine significance between groups. MMD rate was 7.7 per cent (44 of 574). Of this subset of patients, 33 underwent completion axillary dissection, and only two were found to have NSLN-positive disease. Statistical significance was achieved for NSLN positivity when comparing all three nodal groups against one another (χ(2)(2, 572) = 337.084, P = 0.000). Logistic regression showed multifocality and lymphovascular invasion to be significant predictors of NSLN metastasis. NSLN positivity in patients with MMD acts similarly to node-positive disease and therefore cannot completely exclude axillary dissection from therapeutic algorithm.