Ki-67 labeling index is a predictor of postoperative persistent disease and cancer growth and a prognostic indicator in papillary thyroid carcinoma.

BACKGROUND We previously reported that the Ki-67 labeling index (LI) in primary tumors and the thyroglobulin (Tg)-doubling time (DT) were potent prognostic indicators in patients with papillary thyroid carcinoma (PTC). OBJECTIVES To elucidate the relationship between these two factors. METHODS A total of 390 patients with PTC who underwent total thyroidectomy between 1998 and 2004 and in whom the Tg-DT was calculated were enrolled. We determined the Ki-67 LI in primary tumors and compared these values with the patients' clinicopathological factors, postoperative Tg status, Tg-DT, and prognosis. Tg status was categorized by postoperative serum Tg values: biochemically persistent disease (BPD), equivocal state, and biochemical remission. RESULTS The Ki-67 LI was ≤5% in 312 patients (80%), 5%-10% in 48 patients (12%), and >10% in 30 patients (8%). Ki-67 LI was significantly associated with BPD (p < 0.0001). The proportion of BPD patients increased with the higher Ki-67 LI category: 24, 67, and 87%, respectively. The Ki-67 LI had a significant inverse correlation with the Tg-DT (Spearman's ρ = -0.5267, p < 0.0001). Of the 378 patients without distant metastasis at surgery, 68 patients had recurrence, and 6 of the 390 patients died of PTC during the follow-up (mean 88 months). On multivariate analyses, the Ki-67 LI remained an independent predictor of disease-free survival and disease-specific survival when Tg-DT and Tg status were excluded from the analyses. CONCLUSIONS Evaluation of the Ki-67 LI in primary tumors may allow the prediction of the postoperative Tg status, Tg-DT and prognosis of patients with PTC. Published by S. Karger AG, Basel.