Prognostic value of the 8 th edition of the tumor-node-metastasis classification for patients with papillary thyroid carcinoma: a single-institution study at a high-volume center in Japan.

The tumor-node-metastasis (TNM) staging system is most commonly adopted to evaluate the prognosis of patients with thyroid carcinoma. The 8th edition of the TNM staging system, an extensively revised version of the 7th edition, was recently released. We aimed to investigate whether and how well the 8th edition reflects the cause-specific survival (CSS) of patients with papillary thyroid carcinoma by analyzing the cases in 5,892 patients who underwent initial surgery at Kuma Hospital between 1987 and 2005. The median postoperative follow-up duration was 178 months (range: 6-357 months). One patient with T4b disease was excluded from the analysis. Overall, 116 (2.0%) patients died of thyroid carcinoma. The proportion of variance explained (PVE) for CSS in the 7th and 8th editions was 10.69 and 10.97, respectively. Using the 7th edition, CSS of patients with stage IVA and stage III disease was similar (p = 0.32). In contrast, using the 8th edition, CSS was poorer in stage II than in stage I (p < 0.001), in stage III than in stage II (p < 0.001), and in stage IVB than in stage III (p < 0.001). Similar results were observed for disease-free survival. Although we could not establish any objective evidence that the 8th edition is superior to the 7th edition, the 8th edition is simpler and more convenient, as it includes fewer stages and addresses the issue of the 7th edition where stage IVA and III patients had similar prognoses.