Survival Comparison Between 7/8th Edition Of The AJCC/TNM Staging System Of Papillary Thyroid Cancer And The Impact Of Radioactive Iodine Therapy On Survival In Patients With Different Stratifications

Objective: Papillary thyroid cancer is a very common endocrine malignancies.The 8th American Joint Committee on Cancer/Union for International Cancer Control(AJCC/UICC)staging system brought major changes.We conducted this retrospective cohort analysis to assess the changes in 7/8th edition and evaluate their efficacy to predict survival.In addition,we also assessed the difference in radioactive iodine(RAI)benefits from different stratified patients.Methods: The source of the data is from the National Cancer Institute’s Surveillance,Epidemiology,and End Results(SEER)database.From 2006 to 2015,patients with papillary thyroid cancer,including classic papillary thyroid cancer and other variants,were included in our study.Receiver operating characteristic curves and the Harrell’s C concordance index(C-index),Akaike information criterion(AIC)and the Bayesian information criterion(BIC)were used to evaluate the prognostic efficacy of the 7th and 8th AJCC/UICC staging systems.Univariate/multivariate Cox proportional hazards regression models were used to compared overall survival and cancer-specific survival in the 7/8th systems.The interactions between different variables and RAI therapy were further tested by multivariate Cox regression models to compare the survival differences in RAI therapy between the patients in different stratifications.Results: The 8th edition showed higher area under curves and C-index,and lower AIC and BIC.The results of the interaction analysis and group comparisons indicated the differences in effects of RAI therapy in 7/8th edition were similar.Patients with early Stage,early T stage,N0 and subtotal or near total thyroidectomy benefited greatly from RAI therapy.In 8th edition,Stage Ⅲ benefited less from RAI compared with 7th edition.T1 a benefited from RAI,but it benefited less than other T stages.Patients with T3 a benefited more from RAI than T3 b.Conclusion: The 8th edition distinguish better between early and late-stage patients and has better prognosis predictive efficacy.The benefit of RAI treatment in patients is not significantly changed between the 7th/8th edition.In 8th edition,stage Ⅲ/ Ⅳ more accurately differentiate patients with advanced stage.They benefit less compared to patients with early Stage,which may be due to the relative weakening of iodine uptake in advanced-stage tumor cells.T1 a patients benefit less than other T stages.The difference in benefit from RAI in patients with T3 a and T3 b is a novel finding in our study.