RESUMEN
BACKGROUND: The recently implemented AJCC 8th edition TNM staging system for malignant melanoma (MM) changed the definition for T1a and T1b tumours. OBJECTIVES: To analyse differences in disease-free survival (DFS) among patients with thin MM staged according to both AJCC 7th and 8th editions. METHODS: An observational study including 285 patients with cutaneous thin MM (thickness ≤1 mm). Cases were staged as T1a and T1b using both 7th and 8th editions. Neither regional nor visceral diseases were present at diagnosis. DFS curves were generated according to the Kaplan-Meier method. RESULTS: An 8% shift of patients from a T1a towards a T1b stage group was observed after applying the AJCC 8th edition. According to this 8th edition, DFS for T1a patients was significantly longer than for T1b patients (log-rank test; p = 0.005); 5-year DFS for T1a and T1b was 100 and 95%, respectively (Wilcoxon test; p = 0.002). According to the AJCC 7th edition, DFS did not significantly differ for T1a and T1b patients; 5-year DFS for T1a and T1b was 99 and 97%, respectively (p > 0.05). CONCLUSIONS: The AJCC 8th edition seems to be a better tool for staging thin melanomas.