Adrenocortical carcinoma (ACC) is a rare, highly malignant tumor. The aim of the present study is to evaluate the prognostic relevance of a proliferation marker Ki67/MIB1 by immunohistochemistry in 17 cases who underwent resections of the primary tumors and diagnosed to have ACC at Tohoku University Hospital based on the criteria of Weiss during the period from 1976 to 2005. The follow-up periods ranged from 221 days to 10659 days (about 29 years) with the median of 1895 days. The median age at diagnosis was 46 years old, and the mean size of the primary tumors was 7.1 cm with the minimal of 3.5 cm. Ki67/MIB1 labeling index (Ki67/MIB1LI) ranged from 1% to 26%. Kaplan-Meier analysis revealed that patients with Ki67/MIB1LI of 7% or more were associated with significantly shortened disease-free survival (P = 0.0037). The evaluation with Weiss criteria revealed that the median score of Weiss criteria was five, and 13 patients (76.5%) presented positive findings in the criteria of mitotic rate. The survival analysis with Weiss score showed that patients with the scores of 6 or more had both significantly shortened disease-free survival (P = 0.0001) and overall survival (P = 0.0063). The present study has suggested that Ki67/MIB1LI, as well as Weiss score, is a useful predictor for tumor recurrence after resection of the primary tumors in patients with ACC.
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