Ki67 test
The Ki67 test, also known as the Ki67 proliferation index, is a diagnostic tool used to assess the presence of the Ki67 protein in tumors, which indicates cellular proliferation. This protein is found in actively dividing cells and is expressed during all phases of the cell cycle, except the resting phase (G0). The test is primarily utilized in the context of breast and prostate cancers, as well as other tumor types like anaplastic astrocytoma. High levels of Ki67 are associated with more aggressive tumors, making this test useful for determining treatment strategies and evaluating patient response to therapy.
To perform the Ki67 test, a biopsy is conducted to obtain tumor tissue, which is then processed and analyzed using immunohistochemistry to identify Ki67-positive cells. The results are expressed as a percentage, indicating the proportion of proliferating cells, although there is no universally accepted cutoff to define a high Ki67 index. The test's application is somewhat controversial due to variations in techniques and a lack of standardization in treatment protocols based on results. While the Ki67 test is mainly focused on breast cancer prognoses, its relevance in other cancer types continues to be explored within the medical community.
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Ki67 test
ALSO KNOWN AS: Ki67 proliferation index
DEFINITION: The Ki67 protein is present in actively dividing cells. It is expressed during all phases of the cell cycle except for G0 (known as the resting phase). The Ki67 test detects Ki67 in tumors using an immune-based assay that identifies the dividing cells.
Cancers diagnosed or treated: Primarily breast and prostate cancers
Why performed: High Ki67 levels correlate with more aggressive tumors. Characterizing the proliferation rates of tumors via Ki67 expression can help determine what kind of treatment a patient should receive. The Ki67 test can also be used to examine whether a patient has responded to therapy by evaluating changes in cellular proliferation.
Patient preparation: A biopsy is performed to obtain tumor tissue for the Ki67 test. Biopsies can be done either with a needle or through surgery, depending on the size and location of the tumor. If general anesthesia is required for surgery, then the patient must fast prior to the biopsy.
Steps of the procedure: Tumor tissue collected from the biopsy will be sliced very thin and then fixed to a microscope slide. Ki67 will be detected by a method called immunohistochemistry, in which antibodies are used to bind to tumor cells expressing Ki67. The cells are then stained with a colored reagent to identify Ki67+ cells. The tumor sample is examined under a microscope, where cells are counted using an eyepiece grid. Approximately five hundred to two thousand cells are counted and marked as either Ki67+ or Ki67–.
After the procedure: After a needle biopsy, pressure will be applied at the injection site to stop bleeding. For an requiring general anesthesia, the patient will have blood pressure and pulse monitored prior to discharge from the hospital. Transport home must be provided. Open biopsies may also require bed rest for up to twenty-four hours after the procedure, and heavy lifting should be avoided for at least two weeks to allow the to heal.
Risks: Because the Ki67 test is an ex vivo assay (meaning “outside the body”), the only risks are those associated with the biopsy, which include bleeding and infection. Open biopsies may also have risks associated with the surgery (such as scarring) and the anesthesia (such as allergic reactions and changes in blood pressure or heart rate).
Results: Results are reported as a percentage using this equation: ([number of Ki67 + cells / total number of tumor cells] 100). There is no established cutoff to define a high Ki67 proliferation index, but approximately 20 to 30 percent is a common result to be deemed positive. The Ki67 test remains controversial amongst the medical community, which has been unable to standardize treatment plans based on the results. The variables in antibodies chosen, counting methods, and staining procedures have created challenges and presented barriers to widespread use. The test remains relegated mainly to breast cancer prognoses.
Bibliography
DePolo, Jamie. “Understanding Your Pathology Report.” Breastcancer.org, 12 June 2024, www.breastcancer.org/pathology-report. Accessed 13 June 2024.
Inwald, E. C., et al. “Ki-67 Is a Prognostic Parameter in Breast Cancer Patients: Results of a Large Population-Based Cohort of a Cancer Registry.” Breast Cancer Research and Treatment 139.2 (2013): 539–52.
Link, John S., James Waisman, and Nancy Link. The Breast Cancer Survival Manual: A Step-by-Step Guide for Women with Newly Diagnosed Breast Cancer. 5th ed. New York: Henry Holt, 2012.
Pagana, Kathleen Deska, and Timothy James Pagana. Mosby's Diagnostic and Laboratory Test Reference. 11th ed. St. Louis: Elsevier/Mosby.
Tandon, Ankita. “Ki-67 Is a Controversial Prognostic Biomarker in Early-Stage Breast Cancer. Here’s Why.” ASCO Daily News, 4 Jan. 2023. Accessed 13 June 2024.
Torlakovic, Emina E., et al. "Fit-for-Purpose Ki-67 Immunohistochemistry Assays for Breast Cancer." Laboratory Investigation, vol. 104, no. 7, 2024, p. 102076, doi.org/10.1016/j.labinv.2024.102076. Accessed 13 June 2024.