Improved stratification of pT1 melanoma according to the 8th American Joint Committee on Cancer staging edition criteria: A Dutch population-based study.

INTRODUCTION: The 8th American Joint Committee on Cancer (AJCC) staging edition includes revisions regarding pT1 melanomas. We aimed to evaluate the expected impact of this edition on staging and survival in the Dutch pT1 melanoma population.

METHODS: In total, 32,935 pT1 melanoma patients, whose data were retrieved from the Netherlands Cancer Registry between 2003 and 2015, were included in the study. Patients were stratified by the 6th AJCC edition (cohort 1: 2003-2009) and 7th edition (cohort 2: 2010-2015) and all reclassified according to the 8th edition. Stage migration, sentinel lymph node biopsy (SLNB) positivity rates and relative survival were analysed. Agreement between staging systems was calculated by Cohen's kappa coefficient.

RESULTS: In cohort 2, restaging according to the 8th edition led to an increase of 7% in the total number of patients staged pT1b. The kappa score for agreement between the 6th and 8th edition was 0.15 and 0.25 for agreement between 7th and 8th edition. Restaging according to the 8th edition resulted in a higher SLNB positivity rate for pT1b patients than pT1a patients (8% versus 5%, p = 0.08). Relative survival curves were predominantly similar between the staging editions.

CONCLUSIONS: Implementation of the 8th AJCC staging edition will presumably not have major impact on the total number of Dutch pT1b patients. Consequently, the number of patients eligible for SLNB would roughly remain similar. In terms of SLNB positivity, the selection of high-risk pT1 melanoma patients is likely to improve. In addition, the 8th edition criteria for pT1 melanoma seem more workable for pathologists.