Identification of Patients with Intermediate Thickness Melanoma at Low Risk for Sentinel Lymph Node Positivity

Introduction Sentinel lymph node (SLN) biopsy is recommended for all patients with intermediate-thickness melanomas. We sought to identify such patients at low risk of SLN positivity. Methods All patients with intermediate-thickness melanomas (1.01–4 mm) undergoing SLN biopsy at a single institution from 1995–2011 were included in this retrospective cohort study. Univariate and multivariate logistic regression determined factors associated with a low risk of SLN positivity. Classification and regression tree (CART) analysis was used to stratify groups based on risk of positivity. Results Of the 952 study patients, 157 (16.5 %) had a positive SLN. In the multivariate analysis, thickness <1.5 mm (odds ratio [OR] 0.29), age ≥60 (OR 0.69), present tumor-infiltrating lymphocytes (OR 0.60), absent lymphovascular invasion (OR 0.46), and absent satellitosis (OR 0.44) were significantly associated with a low risk of SLN positivity. CART analysis identified thickness of 1.5 mm as the primary cut point for risk of SLN metastasis. Patients with a thickness of <1.5 mm represented 36 % of the total cohort and had a SLN positivity rate of 6.6 % (95 % confidence interval 3.8–9.4 %). In patients with melanomas <1.5 mm in thickness, the presence of additional low risk factors identified 257 patients (75 % of patients with <1.5 mm melanomas) in which the rate of SLN positivity was <5 %. Conclusions Despite a SLN positivity rate of 16.5 % overall, substantial heterogeneity of risk exists among patients with intermediate-thickness melanoma. Most patients with melanoma between 1.01 and 1.5 mm have a risk of SLN positivity similar to that in patients with thin melanomas.