The Ki-67 labeling index (LI) is a test used in pathology to measure how quickly cells in a tissue sample are dividing or growing. It helps in understanding how active, or aggressive, certain cells are, especially in tumours.
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.
This index is used to help pathologists understand the nature of a tumor. It provides valuable information about the growth rate of tumour cells, which is crucial for diagnosis and treatment planning.
The Ki-67 labeling index tells a pathologist how many cells in a sample are in the process of dividing. A higher percentage means more cells are dividing and growing. This information can indicate how aggressive a tumour is.
The definition of a “normal” or “high” Ki-67 labeling index can vary depending on the type of tissue and the specific type of cancer being examined. Generally, a lower Ki-67 index (a smaller percentage of cells showing Ki-67) suggests slower cell growth, which is often seen in healthy, normal tissue and less aggressive tumours. Conversely, a higher Ki-67 index (a larger percentage of cells showing Ki-67) indicates more rapid cell growth, which can be associated with more aggressive tumours. The specific cutoff values for what is considered high or normal can differ based on the cancer type and are determined through clinical guidelines and research.
A high Ki-67 labeling index indicates rapid cell growth, which is a characteristic of many cancers. However, it does not definitively diagnose cancer. Other factors and tests are also considered for a conclusive diagnosis.
The Ki-67 labeling index is particularly useful in certain cancers like breast cancer, brain cancers, and lymphomas. It helps in determining the prognosis (the likely course of the disease) and predicting how the cancer might respond to treatment.
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.