Background: Guidelines for melanoma recommend sentinel lymph node biopsy (SLNB) in patients with melanomas ≥1 mm thickness. Recent single institution studies have found tumors <1.5 mm a low-risk group for positive SLNB. Methods: A retrospective review of the Sentinel Lymph Node Working Group multicenter database identified patients with intermediate thickness melanoma (1.01–4.00 mm) who had SLNB, and assessed predictors for positive SLNB. Results: 3460 patients were analyzed, 584 (17%) had a positive SLNB. Univariate factors associated with a positive SLNB included age <60 (p <.001), tumor on the trunk/lower extremity (p <.001), Breslow depth ≥2 mm (p <.001), ulceration (p <.001), mitotic rate ≥1/mm2 (p =.01), and microsatellitosis (p <.001). Multivariate analysis revealed age, location, and Breslow depth as significant predictors. Patients ≥75 with lesions 1.01–1.49 mm on the head/neck/upper extremity and 1.5–1.99 mm without high-risk features had <5% risk of SLN positivity. Conclusions: Intermediate thickness melanoma has significant heterogeneity of SLNB positivity. Low-risk subgroups can be found among older patients in the absence of high-risk features.
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