New proposed tumor-node-metastasis staging system for medullary thyroid carcinoma based on the Surveillance, Epidemiology, and End Results database.

BACKGROUND Medullary thyroid carcinoma (MTC) has been separated into its own chapter in the 8th edition of the American Joint Committee on Cancer (AJCC) staging system. However, controversies still exist for the staging of MTC. This study aimed to identify prognostic differences among patients with MTC to define a more accurate staging system. METHODS Data on cancer-specific survival from the Surveillance, Epidemiology, and End Results database between 2010 and 2014 were used for this study. Kaplan-Meier (K-M) curves, Cox proportional hazards regression analysis, and mortality per 1000-person-years were used to evaluate the mortality rate to create the new staging system. RESULTS A total of 960 cases were included in this analysis. The mortality rates of 24 different groups, which were classified using T stage (T1-4), N stage (N0-1b), and M stage (M0-1) were assessed using K-M curves. Cox proportional hazards regression analysis and mortality per 1000-person-years were used to classify patients, as stage I (T1-3N0-1aM0, 654, 68.34%), stage II (T1-3N1bM0, 181, 18.91%), stage III (T4N0-1bM0, 58, 6.06%), and stage IV (T1-4N0-1bM1, 64, 6.69%). The hazard ratios of stages II, III, and IV, using stage I as a reference, were 5.281 (95% confidence interval [CI], 1.236-22.562), 20.603 (95% CI, 4.400-96.467), and 55.717 (95% CI, 14.307-216.988), respectively. The mortality rates per 1000-person-years of stages I, II, III, and IV were 2.036 (95% CI, 0.657-6.312), 14.867 (95% CI, 6.679-33.092), 98.287 (95% CI, 54.432-177.478), and 224.199 (95% CI, 146.180-343.860), respectively. CONCLUSIONS Compared with the current AJCC tumor-node-metastasis (TNM) staging system for MTC, this new proposed TNM staging system, which is based on cancer-specific mortality rate analysis, provides more accurate risk stratification and can ensure more rational treatment measures.