Prognostic significance of sentinel node tumor burden in Merkel Cell Carcinoma

Background: A sentinel lymph node biopsy (SLNB) provides important prognostic information in patients with Merkel cell carcinoma (MCC). However, there are no histopathological prognostic factors known to identify high-risk patients amongst those with a positive sentinel lymph node (SLN). In this study we aim to assess the prognostic value of SLN tumor burden and the histological pattern of spread in SLN positive MCC. Methods: The pathology specimen of all patients with MCC who underwent SLNB procedure between 2005 and 2022 was reviewed. SLN tumor burden was measured as the largest diameter of the tumor deposit. Additionally, 5 different histological patterns of sentinel node involvement were scored. Results: There were 131 patients included of whom 46 had a positive SLN. At two years, the overall survival (OS) was significantly higher in patients with a lower than median SLN tumor burden (<0.625 mm) as compared to those with a high SLN tumor burden (90 % vs. 63 %, p = 0.046). There was a non-significant difference in 2-year recurrence-free survival (61 % vs. 37 %, p = 0.082) and disease-specific survival (100 % and 85 %, p = 0.078). A trend towards better OS was observed for patients with a non-solid compared to a solid histological pattern of sentinel lymph node involvement (84 % vs. 60 %, p = 0.061). In a multivariable analysis both immunosuppression (HR 3.9, p = 0.009) and extracapsular extension (HR 8.8, p = 0.002) were significant prognostic factors for OS. Conclusion: MCC patients with a lower SLN tumor burden had a significantly better 2-year OS.