Risk factors of distant metastasis in the follicular variant of papillary thyroid carcinoma.

Background/purpose: The follicular variant of papillary thyroid carcinoma (FVPTC) is the most common variant of papillary thyroid carcinoma (PTC). A previous population-based study revealed its clinical behavior as a mix of classic papillary thyroid carcinoma (C-PTC) and follicular thyroid carcinoma. Whereas locoregional extension was lower in FVPTC than in C-PTC, the distant metastasis rate was higher in FVPTC than in C-PTC. The aim of this study was to evaluate the risk factors of distant metastasis in FVPTC postoperatively.

Methods: A retrospective review of 359 patients with final pathological diagnosis of FVPTC treated at Chang Gung Memorial Hospital between January 2000 and January 2014 was performed. After excluding patients who had inadequate pathological data for analysis or did not attend regular follow up for >1 year, 346 patients were included in this study. Univariate and multivariate statistical analyses were performed to determine the significance of various factors.

Results: Of the 346 patients with FVPTC, 19 (5.5%) had lymph node metastases and 32 (9.2%) had distant metastases. Two positive and one negative risk factors were predictive for distant metastasis using multivariate analysis: angiolymphatic invasion [odds ratio (OR), 3.085; 95% confidence interval (CI), 1.008-9.442], extrathyroidal extension (OR, 3.929; 95% CI, 1.330-11.602), and encapsulation (OR, 0.361; 95% CI, 0.154-0.850).

Conclusion: The presence of angiolymphatic invasion, extrathyroidal extension, or nonencapsulation was associated with distant metastasis in FVPTC in this study. In FVPTC patients, postoperative investigation for distant metastasis may be warranted by the presence of these two positive risk factors or the absence of the one negative risk factor.