Comparison of 8th and 7th editions of TNM staging in terms of mortality, persistent disease, and response to treatment in patients with differentiated thyroid cancer

Abstract

Abstract Objective To compare the eighth and seventh editions of TNM staging (TNM-8 and TNM-7) on disease-related mortality, persistent disease, and response to treatment in patients with differentiated thyroid cancer (DTC). Methods and Materials We studied 400 patients (79% female) with DTC with a mean age of 40.93±14.11 years. TNM staging was recorded according to the 7th and 8th editions and patients were followed for at least 1 year and response to therapy was recorded according to ATA response categorization. Results The mean follow up time was 42.5±15.24 months. Overall, 108 patients (27%) were down-staged using the TNM-8, mainly due to the changes in the age cut-off (14.5%), N (9.25%), and T categorization (3.25%). All patients in stage III and 82.8% in stage IV were down-staged. The mean Tg levels were significantly higher in stages III and IV in TNM-8 compared to TNM-7. Four disease-related death were recorded during follow up, all in stage IV according to TNM-7, while one was in stage II according to TNM-8. One year after treatment, persistent disease was detected in 12% and 77% of patients in stage III according to the 7th and 8th editions, respectively (P= 0.04). Similarly, biochemical incomplete response one year after treatment was seen in 7.3% and 87% in stage III disease using 7th and 8th editions (P = 0.006) that fell to 2.4% and 22% in the last visit respectively (P = 0.04). Conclusion Persistent disease and incomplete response to therapy were more common in stages III and IV in TNM-8 compared to TNM-7. The eighth edition was a better predictor of persistent disease in stages III and IV disease.