The prognostic significance of lymphatic invasion in primary melanoma

Abstract

9050 Background: Lymphatic invasion (LI) is an under-observed phenomenon in primary malignancies that can be better detected by immunostaining and that may associate with prognosis. In this study we sought to test the hypothesis that LI was associated with melanoma-specific survival (MSS) and was an independent prognostic factor. Methods: This study included 277 patients with stage I/II melanomas in vertical growth phase (VGP) who had at least 10 years of follow up. The log-rank test was used to test the study hypothesis - 72 melanoma-specific deaths were needed for 80% power to detect an odds ratio of 2.1. Paraffin sections were stained with antibodies to podoplanin (lymphatic vessels) and S-100 (melanoma cells) to identify LI. Univariate and multivariate Cox models were used to evaluate the prognostic significance of LI. An independent cohort of 106 similar patients was used for validation of the 10-year MSS rates. Results: LI was observed in 44.5% (95% CI: 38.6% - 50.4%) of the melanomas and its presence was significantly associated with thickness, mitotic rate, gender, age, and ulceration (U). The Kaplan-Meier survival curves for those with and without LI were significantly different (log-rank test p=0.022). The final multivariate model for time to MSD identified 4 independent prognostic factors: thickness (HR=1.5, p<0.001), U (HR=2.2 p=0.013), site (HR=3.9, p<0.001) and LI (HR=1.9, p=0.015). These factors were used to define a prognostic tree with 5 risk groups defined by melanomas that were thin (≤1.0mm) with no LI or U; thin with LI but no U; 1–3mm with no U; 1–3mm with U; and >3mm. Respectively, MSS rates were 100%, 88.6%, 77%, 48% and 42%. In the validation set, observed 10-year MSS rates in each risk group were not significantly different from those predicted from the survival curves for the tree-based risk groups. Conclusions: LI is an independent prognostic factor for MSS. Among patients with thin melanomas without U the 10-year MSS was lower for those patients with LI (89%, 95% CI=78% - 99%; n=41) compared to those without (100%, n=78). LI is an important prognostic factor that needs further validation in a population of patients from the sentinel node biopsy era. No significant financial relationships to disclose.