Clinical and pathological predictors of micrometastasis in marginal thickness melanoma.

Abstract

e21585 Background: Sentinel lymph node biopsy (SLNB) remains controversial in patients with localized marginal thickness melanoma (MTM). Nonetheless, micrometastasis (miLN) i.e. the presence of clinically occult lymph node (LN) metastasis, upstages localized tumors to Stage III, indicating the need for more extensive surgical resection and escalated systemic therapy. We aim to identify disease predictors associated with miLN in MTM. Methods: This National Cancer Database (2004-2018) analysis includes patients with T1a/T1b, N0, and M0 (AJCC 8th edition) melanoma (Breslow’s depth: 0.76-1.00 mm). We selected 2 cohorts based on the pathological status of LN metastasis, as per SLNB or elective lymphadenectomy: negative LN versus miLN. Bivariate association of various clinical characteristics and LN status was assessed using Chi-square and Fisher’s exact tests. Significant covariates were integrated into a multivariable logistic regression (MLR) with a backward elimination model to identify the risk factors associated with the presence of miLN. A multivariable Cox regression model with backward elimination compared overall survivor (OS) between both cohorts, adjusting for significantly unbalanced factors. Results: N = 72,945 patients with clinical N0 MTM were identified. N = 68,912 (94.5%) had negative LN and N = 4,033 (5.5%) had miLN on pathology. Ethnicity (p = 0.260), Charlson/Deyo comorbidity score (p = 0.0894) and LDH levels (p = 0.2278) did not significantly vary across cohorts. On MLR analysis, patients with miLN were more likely to be younger and have tumors located outside the head & neck. Tumors with miLN were more likely to show lymphovascular invasion, vertical growth, and a mitotic rate of ≥ 1 but less likely to show positive tumor regression. Ulceration was not an independent risk factor of miLN (p = 0.9305). Multivariable analysis showed that patients with miLN had lower OS rates than those with negative LN (HR = 1.66; 95% CI: 1.45-1.90; p < 0.0001). Conclusions: miLN is associated with a worse prognosis, warranting early recognition and prompt treatment initiation. Despite NCCN guidelines incorporating tumor ulceration into decision-making regarding the need for SLNB in clinical N0 MTM, we show that tumor ulceration was not significantly associated with miLN in MTM. However, patient age, tumor location, tumor mitotic rate, lymphovascular invasion, and vertical growth phase were associated with miLN and thus need to be assessed when considering SLNB.[Table: see text]