Reassessment of Differentiated Thyroid Cancer Patients Using the Eighth TNM/AJCC Classification System: A Comparative Study

Background: Facing the prevailing concept that increased diagnosis with no change in mortality drives the increased incidence of differentiated thyroid cancer (DTC), considerable modifications have been introduced in the new edition of the tumor node metastasis (TNM)/American Joint Committee on Cancer (AJCC) staging system. The aim of this study was to compare a group of DTC patients before and after restaging, by mortality, disease severity, and disease outcomes. Methods: DTC patients (N=433) were restaged according to the eighth TNM/AJCC edition, and the results were compared to the seventh edition for clinicopathologic data, treatment modalities, and disease outcomes. Results: When switched to the eighth edition, 97.5% of patients fell into stage III compared to 76.4% before, and only 11/102 patients remained in stages III-IV. Disease-specific mortality was recorded in 11/433 patients, six of whom were in stages I-II upon restaging, compared to none before (p>0.05). In addition, more recurrences were seen in stages II (p=0.05) and III (p=0.03) using the eighth edition compared to the seventh edition. Stage II was affected the most, with recurrence risk increasing from 29% to 76% (p=0.001) and persistence at last visit from 19% to 43% when switching to the eighth edition (p=0.01). Considering stages I and II together, the recurrence risk increased from 16.7% to 28.2% (p=0.01), lymph node metastases from 1.9% to 26.5% (p=0.01), and persistence at last visit from 10% to 15% (p>0.05). Of the 129 patients in the 45- to 54-year-old age group, 53 shifted to stage I (20 from stage II, 29 from stage III, and 4 from stage IV) and five shifted to stage II (all from stage IV). When comparing this age group in stage II only, the eighth edition showed more lymph node metastases (p=0.001), more distant metastases (p=0.003), higher recurrence risk (p=0.002), and more persistence at the last visit (p>0.05). Conclusion: The eighth TNM/AJCC edition provides a more accurate system to discriminate mortality and persistence in DTC patients. Yet, the severity of disease, especially in the 45- to 55-year-old age group and in stage II patients, should not be underestimated following the downstaging of these patients.