External validation of the American Joint Committee on Cancer melanoma staging system eighth edition using the surveillance, epidemiology, and end results program

Aim The American Joint Committee on Cancer (AJCC) melanoma staging system eighth edition (AJCC-8) was recently released to provide accurate staging reflecting advances in the treatment of melanoma. Using population registry data, this study independently validates and compares the prognostic performance of AJCC-8 to the seventh edition (AJCC-7). Methods We extracted patient-, tumor-related, and survival data from the SEER-18 registry between 2010 and 2015. To assess overall survival (OS) and cancer-specific survival (CSS) for AJCC-7 and AJCC-8, we performed Kaplan-Meier analysis and computed cumulative hazard functions using Nelson-Aalen function. Results Of 126,408 individuals, 59,989 (47%) and 60,411 (48%) had available data for pathological and clinical-stage OS analysis, respectively. The 3-year OS for AJCC-7 among pathologically staged patients was: stage IA 97%, stage IB 95%, stage IIA 87%, stage IIB 76%, stage IIC 57%, stage IIIA 86%, stage IIIB 69%, stage IIIC 50%, and stage IV 24%. The 3-year OS for AJCC-8 patients was similar but was 56% for stage IIIC and 30% for stage IIID. Stage IV individuals with an elevated LDH had worse OS and CSS at all measured time-points up to 60 months compared to those with a normal LDH. Conclusion The discriminatory ability of AJCC-8 and AJCC-7 appear comparable. Changes in AJCC-8 identified stage IIID as a poor prognostic subgroup among stage III patients and elevated LDH in stage IV. However, patients with advanced T-stage, node-negative tumors experienced worse survival compared to those with earlier T-stage, node-positive tumors, and the results of ongoing trials should inform adjuvant therapy in this subset of patients.