Distant metastasis at diagnosis and large tumor size are significant prognostic factors of widely invasive follicular thyroid carcinoma.

In contrast to minimally invasive follicular thyroid carcinoma (FTC), widely invasive FTC is aggressive and is associated with a dire prognosis. However, prognostic factors of widely invasive FTC have not been intensively investigated. In this study, we investigated this issue in a series of 79 widely invasive FTC patients. In the subset of 70 patients who did not show distant metastasis at diagnosis (M0), only a tumor size larger than 4 cm had a prognostic impact on disease-free survival (DFS) both on uni- and multivariate analyses. Regarding the cause-specific survival (CSS) of 79 patients, only distant metastasis at diagnosis (M1) had a significant prognostic value on uni- and multivariate analyses. None of the 70 M0 patients with a tumor measuring 4 cm or less died of FTC. Other clinicopathological features such as age, gender, and oxyphilic carcinoma were of no prognostic value. These findings suggest that 1) M1 is the strongest prognostic factor for CSS of widely invasive FTC patients, and 2) a tumor size larger than 4 cm significantly affects the DFS and CSS of M0 patients. Aggressive therapies with careful follow-up are recommended, especially for these patients.