Introduction: Sentinel lymph node biopsy (SLNB) provides prognostic value in melanoma and guides management. Objective: To evaluate factors associated with SLNB utilization in patients with cT1b melanoma, including clinicopathologic features, gene expression profiling (GEP), and available predictive risk models. Methods: We retrospectively reviewed patients diagnosed with cT1b melanoma from 2010 to 2024 using the University of Vermont Cancer Center registry. Demographic and clinicopathologic data were analyzed. Bivariate tests identified associations; logistic regression determined predictors of SLNB. Among patients who underwent SLNB, predicted SLN positivity was calculated using Melanoma Institute Australia (MIA) and Memorial Sloan Kettering Cancer Center (MSKCC) risk calculators. Model discrimination was assessed using area under receiver operating characteristic curve. Results: Among 212 patients, 135 (64%) underwent SLNB. Younger age (p=0.004) and Breslow thickness >0.8 mm (p<0.001) were associated with SLNB, while cardiac disease (p=0.04) and GEP testing (p=0.004) were inversely associated. On multivariable analysis, older age reduced odds of SLNB (OR per 10-year increase 0.62, 95% CI 0.48–0.81, p<0.001), whereas thickness >0.8 mm increased odds (OR=12.48, 95% CI 5.84–26.64, p<0.001). Only one of eight GEP-tested patients underwent SLNB (OR=0.05, 95% CI 0.01–0.44, p=0.008). In the SLNB subset with complete model inputs, the MIA model demonstrated an AUC of 0.744 (95% CI 0.472–1.000), and the MSKCC model demonstrated an AUC of 0.566 (95% CI 0.254–0.877) with poor correlation between models (ICC=0.102). Conclusions: With a SLNB rate of 64% of cT1b melanoma patients, findings from this study highlight variability in SLNB decision-making for cT1b melanoma.
