Endocrine Abstracts

Introduction: The TNM classification of the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC) is the most widely used thyroid cancer staging system. The 8th edition was published in 2016 and introduced modifications to the N0 classification. Histological analysis is no longer necessary for patients to be classified as N0, as long as there is no evidence of lymph node (LN) metastasis in the preoperative imaging tests or clinical evaluation. Therefore, patients may be classified as N0a (without cytological or histological evidence of LN metastasis) or N0b (without clinical or radiological evidence of LN metastasis). Our study aimed to evaluate and compare the prognosis of patients with differentiated thyroid carcinoma (DTC), classified as N0a or N0b.

Methods/design: This was a retrospective study of 594 patients identified from our institutional database, who underwent surgery for DTC between 2000 and 2014. All patients had: apparently complete tumour resection, absence of LN or distant metastasis at diagnosis and non-aggressive histological variant. The association between variables was evaluated using Shi-square and Student’s T-tests.

Results: All patients were followed for a minimum of 3 years postoperatively (146.3±92 months). The majority of patients were female (88%) and had papillary thyroid carcinoma (89%). Three hundred and forty six patients (58.2%) were classified as N0b and the remainder as N0a (41.8%). Mean age was similar in both groups (51.3 years in the N0a group and 50.4 years in the N1b group, P=0.303). There were no significant differences between N0 classification and tumor size (mean size 16.4 mm vs 18.4 mm, P=0.135), multifocality (24.4% vs 26.3%, P=0.214), extra-thyroid extension (16.7% in both cases, P=0.738), treatment with radioactive iodine (44% vs 51.4%, P=0.1), persistence of disease (1.3% vs 2.9%, P=0.415), recurrence of disease (0.8% vs 0.9%, P=0.99) and disease-specific mortality (0.4% vs 0.3%, P=0.962).

Conclusion: Our results suggest that there is no difference in outcome of patients classified as N0a or N0b, regarding disease specific mortality, recurrence and persistence of disease. Therefore, preoperative clinical and imaging evaluation of the cervical region should play a major role in the staging of DTC patients.