8th edition of AJCC/TNM staging system of thyroid cancer: what to expect.

The 8th edition of AJCC/TNM staging system for differentiated thyroid cancer (DTC) has recently been published. The aim of this study was to compare AJCC/TNM staging 7th and 8th edition in terms of tumor stage distribution in a multicenter, consecutive and prospective cohort of newly diagnosed DTC collected in a web-based observational database. Additional information concerning the extent of minimal extrathyroidal extension was collected. A cohort of 1765 DTC patients (76% females, median age 48 years, 94% papillary histotype) was analyzed. Younger patients (<45 years or <55 years according to 7th and 8th edition, respectively) were in stage II (presence of distant metastases) in 2% of the cases with both classifications. According to TNM 7th edition in patients aged ≥45 years (N=1067), stage distribution was: stage I 595 (56%), stage II 85 (8%), stage III 283 (26%), and stage IV 104 (10%). According to TNM 8th edition in patients aged ≥55 years (N=615) was: stage I 391 (64%), II 193 (31%), III 15 (2%) and IV 16 (3%). The 27% of the patients were downstaged with TNM 8th edition. The majority of newly diagnosed DTC patients are in low-risk stages. An important downstaging is observed applying TNM 8th edition.