Ki-67 is a protein found in the nucleus of cells, which is the control center inside each cell. This protein appears when cells prepare to divide and create new cells, a process known as mitosis or cell division. This protein is not present in resting cells – those that are not in the process of dividing. Pathologists perform a test called immunohistochemistry (IHC) to see cells expressing this protein (these cells are called positive or reactive). By measuring Ki-67 levels, pathologists can gauge how actively cells are dividing, providing insights into the growth behavior of tissues, especially in tumours.

Ki-67 labeling index

The Ki-67 labeling index (LI) is the percentage of cells that are expressing Ki-67. In other words, it is the percentage of all cells that can divide. Pathologists often measure the labeling index in tumours to help them decide if the tumour is benign (non-cancerous) or malignant (cancerous). Cancers are more likely to have a high labeling index. The labeling index is also used to provide information about how a tumour will behave or how it will respond to treatment.

Ki-67 labeling index

About this article

This article was written by doctors to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

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