A prediction model for the presence of axillary lymph node involvement in women with invasive breast cancer: a focus on older women.

Axillary lymph node (ALN) status at diagnosis is the most powerful prognostic indicator for patients with breast cancer. Our aim is to examine the contribution of variables that lead to ALN metastases in a large dataset with a high proportion of patients greater than 70 years old. Using the data from two multicenter prospective studies, a retrospective review was performed on 2,812 patients diagnosed with clinically node-negative invasive breast cancer from 1996 to 2005 and who underwent ALN sampling. Univariate and multivariate logistic regression were used to identify variables that were strongly associated with axillary metastases, and an equation was developed to estimate risk of ALN metastases. Of the 2,812 patients with invasive breast cancer, 18% had ALN metastases at diagnosis. Based on univariate analysis, tumor size, lymphovascular invasion (LVI), tumor grade, age at diagnosis, menopausal status, race, tumor location, tumor type, and estrogen and progesterone receptor status were statistically significant. The relationship between age and involvement of axillary metastases was nonlinear. In multivariate analysis, LVI, tumor size and menopausal status were the most significant factors associated with ALN metastases. Age, however, was not a significant contributing factor for axillary metastases. Tumor size, LVI, and menopausal status are strongly associated with ALN metastases. We believe that age may have been a strong factor in previous analyses because there was not an adequate representation of women in older age groups and because of the violation of the assumption of linearity in their multivariate analyses.