Prognostic impact of extent of vascular invasion in low-grade encapsulated follicular cell-derived thyroid carcinomas: a clinicopathologic study of 276 cases.

Continuous controversy surrounds the predictive value of the degree of vascular invasion (VI) in low-grade encapsulated follicular cell-derived thyroid carcinomas (LGEFCs). Some guidelines advocate conservative therapy in LGEFCs with focal VI. There is therefore a need to assess the survival rates of LGEFC patients with various degrees of VI to better stratify patients for subsequent therapy. Furthermore, the prognostic effect of VI within the different histotypes of LGEFCs is not well known. A total of 276 patients with LGEFCs were subjected to a meticulous histopathologic analysis. They were classified as encapsulated papillary thyroid carcinoma, encapsulated follicular carcinoma (EFC), and encapsulated Hurthle cell carcinoma (EHCC). Of the 276 patients, 24 had extensive VI (EVI) (≥4 foci) and 28 displayed focal (<4 foci) VI. EHCC and EFC showed a much higher rate of EVI than encapsulated papillary thyroid carcinoma. Median follow-up was 6 years. All 14 tumors with adverse behavior harbored distant metastases (DMs), of which 9 had DMs at presentation. All 3 patients without EVI who had aggressive carcinomas harbored DMs at presentation. EVI was an independent predictor of poor recurrence-free survival. Excluding cases with DMs at presentation, only patients with EVI had recurrence, and all relapsed cases were EHCC. EVI is an independent predictor of recurrence-free survival in LGEFCs. EHCC with EVI has a particularly high risk of recurrence. When DMs are not found at presentation, patients with focal VI are at a very low risk of recurrence even if not treated with radioactive iodine.