Age and Lymphovascular Invasion Accurately Predict Sentinel Lymph Node Metastasis in T2 Melanoma Patients

Background. The risk of sentinel lymph node (SLN) metastasis in melanoma is related directly to tumor thickness and inversely to age. The authors hypothesized that for T2 (thickness 1.1-2.0 mm) melanoma, age, and other factors may be able to identify a cohort of patients with a low risk of SLN metastases. Methods. The authors developed logistic regression models to predict positive SLNs in patients undergoing SLN biopsy for T2 melanoma using the National Cancer Database. Classification and regression-tree analysis were used to identify groups of patients with high and low risk for SLN metastases. The prediction model then was applied to a separate data set from a multicenter randomized clinical trial. Results. The study identified 12,918 patients with T2 melanoma undergoing SLN biopsy with clinically node-negative melanoma. In the multivariable analysis, increasing thickness, younger age, lymphovascular invasion (LVI), mitotic rate of 1/mm(2) or more, axial location, and Clark level of 4 or 5 were independent risk factors for SLN metastases. A cohort based on age (> 56 years) and no LVI was identified with a relatively low risk (7.8%; 95% confidence interval 7.2-8.4%) of SLN metastases. The independent data set of 1531 patients with T2 melanoma confirmed these findings. Among elderly patients (age > 75 years) with melanoma 1.2 mm or smaller and no LVI, the risk of a positive SLN was 4.9% (95% confidence interval 3.3-7.1%). Conclusions. Younger age and LVI are powerful predictors of SLN metastases for patients with T2 melanoma. This prediction model can inform shared decision-making regarding whether to perform SLN biopsy for older patients with otherwise low-risk T2 melanoma.