Ki-67 index
Pronunciation: K-I-sixty-seven
Proliferation marker expressed as percentage of Ki-67 positive nuclei. Essential for tumor grading and prognosis in brain neoplasms.
Full Definition
The Ki-67 index is a quantitative measure of cellular proliferation expressed as the percentage of cell nuclei that stain positive for the Ki-67 protein marker. Ki-67 is expressed in actively proliferating cells during all phases of the cell cycle except G0, making it an excellent indicator of tumor growth potential. In neuropathology, the Ki-67 index is a critical component of brain tumor classification and grading according to WHO criteria. Higher Ki-67 indices generally correlate with more aggressive tumor behavior and poorer prognosis. The index is calculated by counting positive nuclei in representative high-power fields and expressing the result as a percentage of total nuclei counted.
Usage
Usage note: Express as percentage and specify counting methodology and number of fields examined.
In Context
- "The Ki-67 index was 25%, supporting a diagnosis of anaplastic astrocytoma." — Brain tumor grading report
- "A low Ki-67 index of 2% was consistent with the benign nature of this meningioma." — Immunohistochemical analysis