Ki-67 / proliferation index

What it is

The Ki-67 index (also called the proliferation index or labeling index) is a measure of the fraction of tumor cells that are actively dividing, determined by a special stain (for the Ki-67 protein) applied to tumor tissue. It helps assess how aggressive a glioma is.

Understanding Ki-67 / proliferation index

Ki-67 is a protein present in cells that are dividing but absent in resting cells. By staining for Ki-67, pathologists can estimate what percentage of the tumor cells are actively proliferating — the Ki-67 index. A higher index indicates more active cell division and suggests a more aggressive, higher-grade tumor, while a lower index suggests a slower-growing tumor. The Ki-67 index supports the assessment of grade and aggressiveness, complementing other features such as mitotic activity and the overall appearance. However, it is interpreted alongside the full picture rather than used as the sole basis for grading, as values can overlap between grades. Understanding the Ki-67 index clarifies a tool that helps gauge how actively a glioma is growing. It is one piece of the diagnostic assessment. Understanding it clarifies a measure of tumor proliferation.

Why it matters

Understanding the Ki-67 index helps patients and families interpret a measure of how actively their glioma is dividing — supporting the assessment of aggressiveness alongside other features.