Evaluation of the 8th Edition TNM Classification for Anaplastic Thyroid Carcinoma

Background: The tumor-node-metastasis (TNM) classification system to categorized anaplastic thyroid cancer (ATC) was revised. Methods: The revised system was evaluated using a large database of ATC patients. Results: A total of 757 patients were analyzed. The proportion and median overall survival values (OS: months) for each T category were T1 (n = 8, 1.1%, 12.5), T2 (n = 43, 5.7%, 10.9), T3a (n = 117, 15.5%, 5.7), T3b (n = 438, 57.9%, 3.9), and T4 (n = 151, 19.9%, 5.0). The OS of the N0 and N1 patients were 5.9 and 4.3, respectively (log-rank p < 0.01). Sixty-three (58.3%) patients migrated from stage IVA to IV B by revision based on the existence of nodal involvement and 422 patients (55.7%) were stratified into stage IV B, without a worsening of their OS (6.1), leaving 45 patients (5.9%) in stage IV A with fair OS (15.8). The hazard ratios for the survival of the patients of stage IV B compared to stage IVA increased from 1.1 to 2.1 by the revision. No change was made for stage IV C (n = 290, 38.8%, 2.8). Conclusion: The revised TNM system clearly indicated the prognoses of ATC patients by extracting rare patients with fair prognoses as having stage IVA disease and categorized many heterogeneous patients in stage IV B.