Factors influencing the number of sentinel lymph nodes identified in patients with breast cancer

Background: Although the sentinel lymph node (SLN) is defined as the first node draining a tumor, multiple nodes are often identified. Few SLNs are required for adequate staging; removal of more may be unnecessary. The objective of this study was to determine factors influencing the number of SLN identified. Methods: The University of Louisville Breast Sentinel Lymph Node Study was used to determine correlates of identifying greater than 4 SLNs by using univariate and multivariate analyses. Results: An SLN was identified in 3,882 of 4,131 patients (94%). The median number of SLN identified was 2 (range 1-18); 90% had ≤4 SLNs identified. Palpable tumors, surgeon inexperience, and dermal injection were associated with greater than 4 SLNs identified. All 3 of these factors remained significant on multivariate analysis. Conclusions: Palpable tumors often have greater than 4 SLNs identified, and the use of intradermal injection increases this probability.