Clinicopathological Significance of Papillary Thyroid Carcinoma Located in the Isthmus: A Meta-Analysis.

ABSTRACT

BACKGROUND: The thyroid isthmus is located directly anterior to the trachea and is covered by the strap muscles. Several studies have suggested that papillary thyroid carcinoma (PTC) in the isthmus is more aggressive and is associated with a poor prognosis. The purpose of this meta-analysis was to assess the clinicopathological characteristics and recurrence rates of PTC in the isthmus compared to PTC at other sites. METHODS: Relevant articles were obtained by searching the PubMed database. A meta-analysis was performed using 11 eligible studies. RESULTS: The rate of extrathyroidal extension was 0.502 (95% confidence interval [CI] 0.239-0.764) and 0.454 (95% CI 0.331-0.582) for isthmus PTC and PTC at other site, respectively; however, the difference in the rates was not statistically significant. Lymphovascular invasion did not significantly differ between isthmus PTC (0.179 [95% CI 0.102-0.297]) and PTC at other sites (0.114 [95% CI 0.066-0.188]). The rate of central lymph node (LN) metastasis was significantly higher in isthmus PTC (0.527 [95% CI 0.435-0.617]) than in PTC at other sites (0.352 [95% CI 0.280-0.432]). No significant difference was observed between the two groups in terms of lateral cervical LN metastasis rate. Isthmus PTC was more likely to have a prominent recurrence rate (0.046 [95% CI 0.022-0.094]) than PTC at other sites (0.010 [95% CI 0.001-0.070]); however, the difference was not statistically significant (because of the small number of included studies). CONCLUSIONS: The results of this meta-analysis indicated that isthmus PTC was associated with an increased risk of central LN metastasis. Isthmus PTC seems to have a slightly higher recurrence rate than PTC at other sites. Therefore, considering the potential of the isthmus location as an unfavorable factor, more attention should be focused on isthmus PTC, and a more aggressive approach such as prophylactic central LN dissection might provide better outcomes in PTC management.