A relook at the 8th edition of the AJCC TNM staging system of anaplastic thyroid carcinoma: A SEER-based study

Objective In the 8th edition American Joint Committee on Cancer (AJCC) tumour-node-metastasis (TNM) staging system (TNM-8), changes have been made regarding anaplastic thyroid carcinoma (ATC) compared with the 7th edition (TNM-7). The major changes are that anaplastic ATC now has the same T stage definitions as differentiated thyroid cancer, and new staging of IVA and IVB is implemented. However, the clinical impact of the new edition for ATC remains unclear due to scarce and conflicting data. In this study, we compared the AJCC TNM-7 and TNM-8 in the same group of patients. Design In this retrospective study, we included patients who were diagnosed with ATC between 2004 and 2015; data were gathered from the Surveillance, Epidemiology and End Results (SEER) database. Methods Overall survival (OS) was evaluated according to T stage and TNM stage according to the 7th and 8th editions. Kaplan-Meier and log-rank testing was used to analyse OS. The effect of potential predictors was estimated using the Cox regression model. Results We included 669 patients in the study. The median age of the cohort was 70 years. During the follow-up, 600 (89.7%) patients died, 528 of whom died of thyroid cancer. The TNM-8 T staging more effectively predicted survival than the 7th edition (proportion of variation explained: 3.53% vs. 1.72%). However, the clinical stage was almost unchanged according to the TNM-8 (proportion of variation explained: 10.69% vs. 10.73%). Conclusions The new T classification is an effective predictor of survival for patients with ATC. The results support the use of T definitions as per those of differentiated thyroid cancer. However, whether lymph node metastasis should be taken into account for defining ATC TNM staging should be reconsidered.

Automated summary

The study compared the impact of AJCC TNM-7 and TNM-8 on patients with ATC. It found that the TNM-8 T staging more effectively predicted survival, but the clinical stage remained almost unchanged. The new T classification is an effective predictor of survival for ATC patients, supporting the use of T definitions as per those of differentiated thyroid cancer.