Association of sentinel lymph node diameter with melanoma metastasis

Background Lymph nodes are an important part of the immune system and the size of the lymph node reflects local immunologic activity. The purpose of this study was to examine the association between sentinel lymph node (SLN) size and the presence of nodal metastasis in patients with melanoma. Methods Retrospective review of a prospectively maintained database of patients undergoing SLN biopsy for cutaneous melanoma between February 1995 and January 2013. The maximum pathologic diameter and the volume of the largest node was used. A nodal diameter of 1.5 cm, included in 2 interquartile ranges of both positive and negative SLNs, was used as the cutoff for multivariate regression. Results Of 1,017 SLN biopsies, 826 (81%) had complete size measurements and were included in the analysis. Patients with a positive SLN were younger (median 50 vs 53 years, P =.032), had deeper primary lesions (2 vs 1.4 mm, P <.001), and had larger SLN volume (.8 vs.6 cc, P =.009) or maximum diameter (1.9 vs. 1.6 cm, P =.03). Sex, pathologic ulceration, mitosis, and the type or location of the primary was not statistically different. On multivariate analysis; age, depth of primary, and both SLN volume and maximum diameter remained significant. An SLN greater than 1.5 cm in maximum diameter has a 60% increased odds ratio of being positive after adjusting for age, sex, and depth of primary lesion (P =.046). Conclusions Larger SLN maximum diameter is associated with nodal positivity independent of age, sex, depth of primary lesion, and location of SLN biopsy. The etiology and significance of larger SLNs warrant further analysis.