Ki-67 is an indicator of progression of neuroendocrine tumors.

No current histological or cytological indices can distinguish reliably malignant from benign tumors in neuroendocrine tumors, including pheochromocytomas, pancreatic endocrine tumors, and carcinoid tumors. We investigated immunohistochemically the expression of Ki-67 in 52 neuroendocrine tumors, including 17 pheochromocytomas, 9 pancreatic endocrine tumors, 23 carcinoid tumors, 2 neuroendocrine carcinomas (NEC), and 1 neuroblastoma with liver metastasis. Of the 52 tumors, distant metastasis was observed in 4 pheochromocytomas, 2 pancreatic endocrine tumors, 4 carcinoids, 2 NEC, and 1 neuroblastoma. We classified these tumors into 3 groups; Groups A, B, and C, depending on the number of Ki-67-positive cells counted under a 200 x magnified field. Expression of Ki-67 was extremely high in group A (> 50 labeled nuclei/field), moderately high in group B (20-50 labeled nuclei), and very low in group C (< 10 labeled nuclei). There was a significant correlation between expression of Ki-67 and tumor progression. The tumors in group A progressed rapidly with the worst outcome; the tumors in group B progressed slowly but with a bad outcome; and the tumors in group C had no metastasis and a good prognosis. Ki-67 is an excellent indicator to assess progression of neuroendocrine tumors.