Endocrine Abstracts

Introduction: Thyroid isthmus has lack of normal parenchyma, and it connects both of thyroid lobes with lymphatic drainage. It is known that isthmic papillary thyroid cancer (PTC) presents frequent extrathyroidal extensions (ETE), multifocality and lymph node involvement. Therefore, many surgeons prefer total thyroidectomy and central compartment neck dissection (CCND) for the radical treatment of PTC located in thyroid isthmus. The purpose of this study is to figure out the clinical implication of isthmic tumor location in PTC compared with PTC located in unilateral thyroid lobe.

Materials and Methods: A total 1500 patients with PTC who underwent total thyroidectomy and lymph node dissection were reviewed. 160 were isthmic PTC patients (isthmic cancer group). 1340 were patients with PTC located in unilateral thyroid lobe and 1:5 propensity score matching in age, sex and tumor size were performed. Finally, 800 patients (matched-unilateral cancer group) were selected to compare with isthmic cancer group.

Results: After matching, the median follow up period of total patients was 122 months. 10-year cumulative RFS rate were 99% for isthmic cancer group and 96% for matched-unilateral cancer group (P = 0.260), respectively. There were no differences in age, sex, tumor size, ETE, tumor multifocality and the number of metastatic lymph node between two groups. However, the ratio of patients with lateral neck node metastasis was lower in isthmic cancer group (P = 0.032) and it mainly occurred bilaterally (P < 0.001) in comparison with matched-unilateral cancer group. The tumor location of isthmus did not increase the risk of ETE, lymph node metastasis and tumor multifocality in multivariate analysis. It did not worse RFS in Cox regression, neither.

Conclusion: The isthmic location is not an independent risk factor in papillary thyroid carcinoma, therefore, it is necessary to reconsider the preference of total thyroidectomy in thyroid isthmus cancer.