Ki-67 index
Pronunciation: KEY-sixty-seven index
A proliferation marker used to grade neuroendocrine tumors based on the percentage of dividing cells.
Full Definition
The Ki-67 index is a proliferation marker that measures the percentage of tumor cell nuclei positive for the Ki-67 antigen, which is expressed during active phases of the cell cycle. In neuroendocrine tumor classification, the Ki-67 index is crucial for determining tumor grade and prognosis according to WHO criteria. Grade 1 (G1) tumors have a Ki-67 index less than 3%, Grade 2 (G2) tumors range from 3-20%, and Grade 3 (G3) tumors exceed 20%. The index is determined through immunohistochemical staining and manual counting or automated analysis of at least 500 tumor cell nuclei in areas of highest labeling density. Higher Ki-67 values correlate with more aggressive tumor behavior and worse prognosis.
Usage
Usage note: Essential for WHO grading system of neuroendocrine tumors.
In Context
- "The Ki-67 index was 8%, classifying this as a Grade 2 neuroendocrine tumor." — Pathology report
- "Tumor grading revealed a Ki-67 index of 25%, indicating high-grade neuroendocrine carcinoma." — Histopathology report