Development of a prognostic model for patients with nodular melanoma of the lower extremities: a study based on the SEER database.

Lower extremity nodular melanoma (NM) is a common malignant tumor with a poor prognosis. We aims to identify the prognostic factors and develop a nomogram model to predict overall survival (OS) in patients with lower extremity NM. A total of 746 patients with lower extremity NM were selected and randomly divided into a training set (522 cases) and a validation set (224 cases) from the Surveillance, Epidemiology, and End Results(SEER) database. The training set underwent univariate and multivariate Cox regression analyses to identify independent prognostic factors associated with patient outcomes, and to develop a nomogram model. The effectiveness of the nomogram was subsequently validated using the validation set. Multivariable Cox regression analysis of the training set indicated that age, ulceration, radiotherapy, chemotherapy, primary site of first malignant tumor, and Breslow thickness were independent variables associated with OS. In the training set, the area under the curve (AUC) of the nomogram for predicting 3-year and 5-year OS was 0.796 and 0.811, respectively. In the validation set, the AUC for predicting 3-year and 5-year OS was 0.694 and 0.702, respectively. The Harrell's C-index for the training set and validation set were 0.754 (95% CI: 0.721-0.787) and 0.670 (95% CI: 0.607-0.733), respectively. Calibration curves for both training and validation sets showed good agreement. In this study, we develop and validate a nomogram to predict OS in patients with lower extremity NM. The nomogram demonstrated reasonable reliability and clinical applicability. Nomograms are important tools assessing prognosis and aiding clinical decision-making.