Long Term Outcome of Minimally Invasive Follicular Thyroid Carcinoma according to Risk Group Stratification

Purpose: This study evaluated the risk factors for distant metastasis in patients with minimally invasive follicular thyroid carcinoma (MIFTC) and compared distant metastasis-free survival (DMFS) rates between the groups divided based on the number of involved risk factors. Methods: Patients were divided into 4 groups based on the number of involved risk factors; group 0 with no risk factor, group 1 with any one risk factor, group 2 with any 2 risk factors, and group 3 with all risk factors. Results: The 195 patients were enrolled in this study. Distant metastasis was detected in 15 patients (7.7%). In the multivariate analysis, age ≥ 45 years (hazard ratio [HR]=5.95; 95% confidence interval [CI]=1.44&#8211;24.55; P=0.014), primary tumor size >4.0 cm (HR=4.79; 95% CI=1.18&#8211;19.33; P=0.028), and extensive vascular invasion with ≥4 foci (HR=19.63; 95% CI=5.18&#8211;74.39; P<0.001) were identified as independent risk factors for distant metastasis. Group 1 tended to have poorer DMFS rates as compared with group 0, but there was no significant difference (P=0.069). DMFS rates of group 2 and 3 were significantly poorer than those of group 1 (P<0.001 and <0.001, respectively). DMFS rates of group 3 were also significantly poorer than those of group 2 (P=0.004). Conclusion: MIFTC patients with no or only one distant metastasis-related risk factor may become candidates for close observation without additional treatments with respect to DMFS rates.