External validation of a prognostic model to predict survival of patients with sentinel node-negative melanoma

Background Identifying patients with sentinel node-negative melanoma at high risk of recurrence or death is important. The European Organisation for Research and Treatment of Cancer (EORTC) recently developed a prognostic model including Breslow thickness, ulceration and site of the primary tumour. The aims of the present study were to validate this prognostic model externally and to assess whether it could be improved by adding other prognostic factors. Methods Patients with sentinel node-negative cutaneous melanoma were included in this retrospective single-institution study. The beta values of the EORTC prognostic model were used to predict recurrence-free survival and melanoma-specific survival. The predictive performance was assessed by discrimination (c-index) and calibration. Seeking to improve the performance of the model, additional variables were added to a Cox proportional hazards model. Results Some 4235 patients with sentinel node-negative cutaneous melanoma were included. The median follow-up time was 50 (i.q.r. 18 center dot 5-81 center dot 5) months. Recurrences and deaths from melanoma numbered 793 (18 center dot 7 per cent) and 456 (10 center dot 8 per cent) respectively. Validation of the EORTC model showed good calibration for both outcomes, and a c-index of 0 center dot 69. The c-index was only marginally improved to 0 center dot 71 when other significant prognostic factors (sex, age, tumour type, mitotic rate) were added. Conclusion This study validated the EORTC prognostic model for recurrence-free and melanoma-specific survival of patients with negative sentinel nodes. The addition of other prognostic factors only improved the model marginally. The validated EORTC model could be used for personalizing follow-up and selecting high-risk patients for trials of adjuvant systemic therapy