Ki-67 is a protein found in cells that are actively growing and dividing (proliferating). Normal prostate cells proliferate slowly and do not produce, or ‘express,’ Ki-67. However, in prostate cancer cells that are actively proliferating, Ki-67 is expressed in large amounts. Prostate tumors that contain lots of cells expressing Ki-67 are generally more aggressive. Ki-67 overexpression also points to poorer prognosis and a higher chance of metastases and recurrence. Ki-67 is a prognostic marker in prostate cancer and its expression does not necessarily point to a specific treatment strategy.
The expression of Ki-67 can be determined in prostate tissue specimens by immunohistochemical staining. This process uses proteins called antibodies to label cells that express Ki-67. The number of positive Ki-67 cells can be determined manually or by using a computer program. Immunohistochemical results are typically reported as a percentage of tumor cells expressing Ki-67, with the values ranging from 0% to 100%. This percentage may be referred to as the proliferation index.
The test for Ki-67is not a screening test, therefore, your doctor may or may not recommend it. Some medical facilities may perform Ki-67 testing onsite or the tumor specimen may be sent out to a specialized lab.
The Ki-67 protein is closely linked to a process known as the cell cycle, which can be thought of as a series of changes that a single cell undergoes as it prepares to divide into two cells. Scientists divide the cell cycle into different phases. Ki-67 is not found in cells that are at rest (G0 phase) or in the earliest stages of the cell cycle (G1 phase). Ki-67expression begins at the end of the G1 phase and increases as cells begin to duplicate their DNA during the synthesis (S phase), until they divide into two cells. In prostate cancer tumors, abnormal Ki-67 expression is associated with higher Gleason scores and more aggressive cancers as well as higher rates of recurrence and metastases.
In addition to prostate cancer, the prognostic potential of Ki-67 expression has been reported in breast, brain, bladder, and colon cancers.
There are no targeted treatments for Ki-67. It serves as a prognostic marker in prostate cancer and its expression does not necessarily point to a specific treatment strategy.
The U.S. Food and Drug Administration (FDA) has not approved any treatments that target Ki-67.
A recent study suggested that taking vitamin D daily decreases the levels of Ki-67 expression in prostate tumors. Although this study did not directly show that the proliferation of the tumor cells was inhibited, it does hold some promise for prostate tumors that are rapidly growing and dividing. It is important to note that further studies are needed to validate these findings. Before beginning a daily vitamin D regimen, you should discuss it with your doctor.