Predictors of regional nodal disease in patients with thin melanomas

Background: Most melanoma patients present with thin ( <= 1.0 mm) lesions. Indications for sentinel lymph node (SLN) biopsy are not well defined for this group. Previously, we reported an association between mitotic rate (MR) and SLN positivity in these patients. The study was limited by a relatively small sample size and low statistical power. In this study, we evaluated a large population of patients with thin melanoma from the pre-SLN era to identify predictors of regional nodal disease (RND) that may serve as a surrogate for SLN positivity. Methods: Eight hundred eighty-two patients evaluated between 1972 and 1991 were included in the study. Univariate and multivariate regression analyses were performed by using clinical and histological data to identify factors associated with RND. A multivariate logistic regression model was developed and applied to the previously reported group of patients with thin melanomas who underwent SLN biopsy between 1996 and 2004 for validation. Results: Thirty-eight patients (4.3%) had evidence of RND. In the multivariate analysis, a MR > 0, vertical growth phase (VGP), male sex, and ulceration were statistically significant predictors of RND. Patients at the highest risk according to a classification tree analysis (VGP and MR > 0) had an RND rate of 11.9%. The regression model developed predicted well the SLN status in the validation sample. Conclusions: Investigation of a large pre-SLN population identified MR > 0, ulceration, VGP, and male sex as independently predictive of RND in patients with thin melanomas. These factors may help to identify subgroups of these patients that have clinically significant risks of SLN positivity.