Clinicopathological, immunohistochemical factors and recurrence associated with extrathyroidal extension in papillary thyroid microcarcinoma

Background and Aims: Extrathyroidal extension (ETE) is one of the most important factors correlated to poor outcome of papillary thyroid carcinoma (PTC). However, the role of ETE in the prognosis of papillary thyroid microcarcinoma (PTMC) and the factor associated with ETE of PTMC are unclear. We investigated clinicopathological, immunohistochemical factors associated with ETE of PTMC to identify whether PTMC with ETE would have more adverse prognostic factors and higher risk for recurrence. Setting and Design: We enrolled patients performed thyroidectomy due to PTC between January 2003 and June 2008 and selected patients diagnosed with PTMC among them. We investigated numerous clinicopathological, immunohistochemical factors of selected patients. Materials and Methods: Data from 325 patients diagnosed with conventional PTMC by intraoperative frozen section and final pathology were recorded retrospectively. Statistical Analysis Used: A χ² test or an independent two-sample t-test, multiple logistic regression analysis, the Kaplan-Meier method, and log-rank test. Results: Thirty-four percent of patients (325 of 952) had PTMC on final pathology. Among them, the number of patients with and without ETE was 91 and 234, respectively. On both univariate and multivariate analysis; ETE of PTMC correlated with size (P < 0.001); tumor, node, and metastasis (TNM) staging (P = 0.001); multifocality (P = 0.001); lymph node metastasis (P < 0.001); radioactive iodine (RAI) therapy (P = 0.001); and recurrence (P = 0.037). Conclusions: ETE of conventional PTMC is associated with size, multifocality, lymph node metastasis, and recurrence. More extensive surgery should be considered for patients having ETE identified by intraoperative frozen sections, preoperative imaging, and intraoperative finding and other high risk factors.