Sentinel Lymph Node Biopsy and Isolated Tumor Cells in Invasive Lobular Versus Ductal Breast Cancer

Background Sentinel lymph node (SLN) biopsy is the standard of care for axillary staging in invasive breast cancer. The introduction of SLN biopsy with an extensive pathology examination, in addition to the introduction of the 2002 TNM classification, led to different axillary classification outcomes. We evaluated the effect of axillary staging procedures and subsequent axillary nodal status in patients with invasive lobular carcinoma (ILC) versus invasive ductal carcinoma (IDC) from 1998 to 2013. Materials and Methods The use of SLN biopsy and the nodal status distribution were analyzed in patients with stage T1-T2 ILC and IDC. Logistic regression analysis was performed to determine the independent effect of histologic type on the probability of the presence of isolated tumor cells (ITCs), micrometastases, and macrometastases. Results A total of 89,971 women were diagnosed, 10,146 with ILC (11%) and 79,825 with IDC (89%). The patients who had undergone SLN biopsy were more frequently diagnosed with ITCs than were those who had undergone axillary lymph node dissection only (odds ratio, 8.8; 95% confidence interval, 7.0-11.2). In 2013, the proportion of patients with ITCs in the axillary nodes was 8% in those with ILC and 4.4% in those with IDC. Patients with ILC were significantly more likely to have ITCs in their axillary lymph nodes than were patients with IDC (odds ratio, 1.8; 95% confidence interval, 1.6-2.0). Conclusion With the introduction of SLN biopsy and the renewed 2002 TNM classification, patients with ILC have been more frequently diagnosed with ITCs than have patients with IDC. The clinical consequence of this finding must be established from further research.