Performance of the MSKCC Nomogram for Predicting Sentinel Lymph Node Positivity in Cutaneous Melanoma: A Single-Center Retrospective Validation in a Romanian Cohort

Background and Objectives: Sentinel lymph node biopsy (SLNB) is the standard procedure for regional nodal staging in patients with clinically localized cutaneous melanoma. However, most patients undergoing SLNB have negative sentinel lymph nodes, highlighting the need for predictive tools to optimize selection. The Memorial Sloan Kettering Cancer Center (MSKCC) nomogram estimates the probability of sentinel lymph node metastasis using clinicopathological variables. This study evaluated the discrimination, calibration, and net benefit of the MSKCC nomogram in a Romanian cohort of patients with cutaneous melanoma. Materials and Methods: We conducted a retrospective, single-center cohort study including 117 patients with primary cutaneous melanoma who underwent SLNB between 2020 and 2025. The predicted probability of sentinel lymph-node (SLN) metastasis was calculated using the official MSKCC nomogram, and histopathological SLN status served as the reference standard. Discrimination was evaluated using receiver operating characteristic analysis, and threshold-based classification was assessed at predicted risks of 5%, 10%, and the exploratory Receiver Operating Characteristic (ROC) curve-derived threshold of 19%. Calibration was assessed using the observed-to-expected ratio and the calibration intercept and slope, and net benefit was evaluated by decision curve analysis. Results: Patients with positive sentinel lymph nodes had higher MSKCC-predicted risks than patients with negative nodes (median 20.0% vs. 10.0%; p = 0.0004). The MSKCC score was associated with SLN positivity (OR 1.065 per 1-percentage-point increase; 95% CI 1.026–1.106; p = 0.0011). The model showed moderate discrimination (AUC = 0.714; 95% CI 0.614–0.814). At the 5% threshold, 24 patients (20.5%) were classified below the threshold, and no SLN-positive case was observed in this subgroup; however, the subgroup was small. Higher thresholds classified more patients below the biopsy threshold but reduced sensitivity. The nomogram underestimated the observed risk (mean predicted 15.6% vs. observed 26.5%; observed-to-expected ratio 1.70, 95% CI 1.15–2.41; calibration slope 0.89). Compared with SLNB for all patients, nomogram-based selection yielded a net reduction of 20.5 biopsies per 100 patients at the 5% threshold but no net benefit at the 10% threshold. Conclusions: In this cohort, the MSKCC nomogram showed moderate discrimination for SLN positivity but underestimated the absolute risk of SLN metastasis. It may be useful as an additional tool in selected or borderline cases, but it should be applied with caution and should not replace established clinicopathological criteria and guideline-based SLNB recommendations. Validation in larger multicenter cohorts, including recalibration, is required before any risk threshold can be recommended.