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.