This study developed and validated an online risk calculator and nomogram to predict sentinel lymph node (SLN) positivity in patients with Merkel cell carcinoma (MCC). The tool incorporates multiple clinicopathologic variables including tumor size, anatomical location, and patient demographics to estimate the probability of nodal involvement. The calculator provides clinicians with a quantitative tool to guide SLNB decision-making and patient counseling for MCC, supporting personalized management approaches.

An externally validated nomogram can predict SLN positivity in MCC using readily available clinicopathologic variables.

Tumor size, anatomical location, and immunosuppression status are among the strongest predictors of nodal involvement in MCC.

This risk calculator can aid shared decision-making regarding SLNB in MCC, particularly for borderline cases.