Ki67
Definition
Ki67 is a molecule that can be easily detected in growing cells in order to gain an understanding of the rate at which the cells within a tumor are growing.
Purpose
Detection of Ki67 is carried out on biopsies, samples of tumor tissue. The goal of this assay is to evaluate an important characteristic of the cells within the tumor, the percentage of tumor cells that are actively dividing and giving rise to more cancer cells. The number obtained through this examination is termed the S-phase, growth, or proliferative fraction. This information can play an important part in deciding the best treatment for a cancer patient.
Precautions
This test is performed on tissue or cells that have been removed during the initial surgery or diagnostic procedure used to determine the precise nature of the cancer. It usually does not require any new surgery or blood draw on the patient and, so, does not entail any additional precautions for the patient.
Description
Cancer is a group of diseases characterized by abnormal, or neoplastic, cellular growth in particular tissues. In many instances this growth is abnormal because cells are growing more rapidly than is normal. This unregulated growth is how a tumor is formed. A tumor is more or less a collection of cells that grow more rapidly than the surrounding normal tissue. Most importantly, this difference in growth rate is central to how many cancer drugs, termed cytotoxic agents, work. The ability of these drugs to eliminate cancer cells depends on their ability to kill cells that are actively proliferating, but do less damage to cells that are not actively dividing. This makes it useful to know how actively the cells in tumor are growing compared to the surrounding tissue. The measurement of Ki67 is one of the most common ways to measure the growth fraction of tumor cells. This molecule can be detected in the nucleus of only actively growing cells.
Analysis of Ki67 in tumors is accomplished by a pathologist who examines a piece of the tumor tissue using special techniques. The technique used is termed immunocytochemistry. This involves the preparation of a histologic section, a very thin piece of tumor tissue placed on a glass microscope slide. These kinds of tissue sections are used in the diagnosis of cancer. In the case of Ki67 assays, the section is incubated with antibodies that can react with the Ki67 molecule, and then treated with special reagents that cause a color to appear where antibody has bound. In this way, when the pathologist looks at the section using a microscope the fraction of growing cells, whose nuclei are stained for Ki67, can be determined for the tumor cells and compared with the normal tissue. In some instances, depending on the particular type of cancer, the pathologist might feel it more appropriate to use a different technique to assess the growth fraction for a specific tumor or leukemia.
