Abstract: Background and purpose: The TNM staging system was updated to eighth edition (TNM-8) in 2017 by American Joint Committee on Cancer (AJCC). The purpose of this study was to compare staging results of the papillary thyroid carcinoma (PTC) using TNM-8 and seventh edition (TNM-7) staging systems. Methods: A total of 4 265 patients who were diagnosed with PTC and underwent primary surgery at the Peking Union Medical College Hospital from 2013 to 2015 were reviewed. The extent of surgery included lobectomy and ipsilateral lymph node dissection at least. According to age, gender, tumor size, extent of invasion, lymph node metastasis and distant metastasis, TNM-7 and TNM-8 staging systems were used for staging, and the results were compared. Results: A total of 4 265 patients (1 069 males and 3 196 females) were included. According to TNM-7 system, the number of patients with stage Ⅰ, Ⅱ, Ⅲ, Ⅳa, Ⅳb and Ⅳc were 3 093 (72.50%), 23 (0.54%), 942 (22.09 %), 199 (4.67%), 1 (0.02%) and 7 (0.16%), respectively. Using TNM-8 system, the number of patients with stage Ⅰ, Ⅱ, Ⅲ and IVb were 3 996 (93.60%), 259 (6.00%), 9 (0.20%) and 1 (0.02%), respectively. A total of 1 163 patients (27.3%) were down-staged. The reasons for the down-staging included the adjustment of age to 55 years (781 cases, 67.1%), the adjustment of TNM staging rules (265 cases, 22.8%), and the adjustment of T staging rules (117 cases, 10.1%). In 3 059 microcarcinoma patients, the numbers of Ⅰ-Ⅳ patients by TNM-7 were 2 323 (75.94%), 3 (0.10%), 649 (21.22%) and 84 (2.70%), respectively. By TNM-8, the numbers were 2 917 (95.30%), 138 (4.50%), 3 (0.10%) and 1 (0.03%), respectively. Conclusion: With the TNM-8, the proportion of patients with stage Ⅲ-Ⅳ is significantly decreased. This feature is even more prominent in patients with microcarcinoma, and can better indicate the severity of the disease.

Key words: Papillary thyroid carcinoma, TNM staging system, Eighth edition