New Insights on the Importance of the Extent of Vascular Invasion in Widely Invasive Follicular Thyroid Carcinoma

Background This study aimed to investigate the association between the extent of vascular invasion (VI) and the outcome of widely invasive follicular thyroid carcinoma (WI-FTC). Methods The records of 107 patients with WI-FTC confirmed by surgical specimens from January 2005 to December 2016 were retrospectively reviewed. Results Among the 107 patients with WI-FTC, those with a VI of < 4 (n = 62) and ≥ 4 (n = 45) had a 10 year cause-specific survival (CSS) rate of 97.7% and 89.4% ( p = 0.008), respectively. Univariate analysis identified M1 ( p = 0.001), and the number of VI of ≥ 4 as significant negative prognostic factors for CSS. Multivariate analysis identified M1 (hazard ratio [HR] = 9.366) as independent negative prognostic factor for CSS. Among the 72 patients with M0 WI-FTC, those with a VI of < 2 (n = 33) and ≥ 2 (n = 39) had a 10-year distant metastasis-free survival (DMFS) rate of 96.8% and 56.8% ( p = 0.001), respectively. Univariate analysis identified age ≥ 55 years ( p = 0.011), presence of VI, the number of VI of ≥ 2, and resection margin status ( p < 0.001) as significant negative prognostic factors for DMFS. Multivariate analysis identified the number of VI ≥ 2 (HR = 9.137), and resection margin status (HR = 5.853) as independent negative prognostic factors for DMFS. Conclusions It may be unnecessary that WI-FTC with curative resection margin status and a VI of < 2, especially in capsular invasion only, routinely undergo completion thyroidectomy and postoperative ablation.