Prognostic impact of Ki-67 labeling index in minimally invasive follicular thyroid carcinoma.

We investigated the prognostic impact of the Ki-67 labeling index (LI) in minimally invasive follicular thyroid carcinoma (FTC). We enrolled 192 patients (including four with distant metastasis at diagnosis) who were pathologically diagnosed as having minimally invasive FTC between 1998 and 2007 at Kuma Hospital. When the Ki-67 LI was higher than 5% in the hot area, we regarded it as a high Ki-67 LI. In a univariate analysis, patient age (≥45 years), high-frequent vascular invasion (≥4 in H&E specimens), and high Ki-67 LI significantly predicted the disease-free survival (DFS) of the patients. Since none of the patients <45 years old showed a recurrence, we performed a multivariate analysis of variables other than patient age. In the multivariate analysis including the presence of vascular invasion, high Ki-67 LI was an independent predictor of carcinoma recurrence. However, in the multivariate analysis including high-frequent vascular invasion, only high-frequent vascular invasion independently affected the DFS. These findings suggest that the Ki-67 LI has a rather strong prognostic value for the DFS of patients, although its impact was less than those of patient age and high-frequent vascular invasion.