A new cell is created when an old cell divides and becomes two cells. For most cells in our body this process is called mitosis. However, not all cells are able to divide. Ki-67 is a test pathologists perform to look for dividing cells. The test allows pathologists to see a protein made by dividing cells.
Ki-67 is a type of test called immunohistochemistry. Immunohistochemistry allows pathologists to see the proteins inside cells.
The proliferation index or proliferation rate is the percentage of cells that are making Ki-67. In other words, it is the percentage of all cells that can divide. Pathologists often measure the proliferation 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 proliferation index.
The number of cells that show Ki-67 is also used to provide information about how a tumour will behave or how it will respond to treatment.
Another name for Ki-67 is MIB-1.