Construction and validation of a prognostic nomogram for primary vulvar melanoma: a SEER population-based study

BACKGROUND Primary vulvar melanoma was an aggressive and poorly understood gynecological tumor. Unlike cutaneous melanoma, the incidence of vulvar melanoma was low but the survival was poor. There were no standard staging system and no census on treatment strategies of vulvar melanoma. Therefore, we aimed to conduct and validate a comprehensive prognostic model for predicting overall survival of vulvar melanoma and provide guidance for clinical management. METHODS Patients diagnosed with vulvar melanoma between year 2004 and 2015 from Surveillance, Epidemiology, and End Result (SEER) database were randomized to training cohort and validation cohort. Multivariate survival analysis was performed to screen for independent factors of survival. A nomogram was established to predict overall survival of vulvar melanoma. Receiver operating characteristic curve and calibration plot were performed to verify the discrimination and accuracy of the model. The decision curve analysis was performed to verify the clinical applicability of the model. RESULTS Total 737 patients with vulvar melanoma were randomized to the training cohort (n = 517) and the validation cohort (n = 220). Nomogram including age, race, tumor site, depth of tumor invasion, lymph node status, distant metastasis, tumor size, surgery, chemotherapy and radiotherapy was established and validated. The c-indexes for SEER stage, American Joint Committee on Cancer stage and this model were 0.561, 0.635 and 0.826, respectively. The high-risk group scored by this model had worse survival than the low-risk group (P < 0.001). Decision curve analysis revealed this model was superior in predicting survival. CONCLUSIONS Our model was deemed to be a useful tool for predicting overall survival of vulvar melanoma with good discrimination and clinical applicability. We hoped this model would assist gynecologists in clinical decision and management of patients diagnosed with vulvar melanoma.