Prognostic Significance of Ki-67 Labeling Index in Papillary Thyroid Carcinoma

Background Ki-67 is a useful tool for evaluating cell proliferative activity in various tumors. Although the utility of Ki-67 labeling index (LI) to diagnose thyroid neoplasms has been investigated, little is known regarding the relationship between Ki-67 LI and the biological behavior of papillary thyroid carcinoma. In this study, we examined Ki-67 in 371 patients with papillary thyroid carcinoma to elucidate this issue. Methods A total of 371 patients with papillary carcinoma who underwent initial and locally curative surgery between 1996 and 1997 were enrolled in this study. We immunohistochemically investigated Ki-67 LI in their primary lesions and compared this finding with various clinicopathological features, including patient prognosis. Results Ki-67 LI was ≤1% in 213 patients (57%) and among the remaining 158, 35 showed Ki-67 LI >3%. Ki-67 LI was associated with patient age, massive extrathyroid extension, and distant metastasis at surgery. Of 363 patients without distant metastasis at surgery, 54 (15%) showed carcinoma recurrence during follow-up (average 124 months) and the disease-free survival (DFS) of patients with Ki-67 LI >1% was significantly worse than that of those with Ki-67 LI