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 <1% ( p < 0.0001). On multivariate analysis, Ki‐67 LI was recognized as an independent prognostic factor for the DFS of patients. Although only eight patients died of carcinoma in our series, patients with Ki‐67 LI >3% showed a significantly worse cause‐specific survival (CSS) than those with Ki‐67 LI <3% ( p < 0.0001). Conclusions Careful evaluation of Ki‐67 LI in primary lesions can predict DFS and CSS of patients with papillary thyroid carcinoma.