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What is the Ki-67 Tumor Marker Test for Breast Cancer?

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Updated May 16, 2014

Question: What is the Ki-67 Tumor Marker Test for Breast Cancer?
Ki-67 is a cancer antigen that is found in growing, dividing cells but is absent in the resting phase of cell growth. This characteristic makes Ki-67 a good tumor marker. This test is done on a sample of tumor tissue, to help predict your prognosis.
Answer:

About the Ki-67 Tumor Marker

Although the Ki-67 test is not always used for breast cancer, many studies have been done to determine its value as a tumor marker test. The researchers agreed that high levels of Ki-67 indicate an aggressive tumor and predict a poor prognosis. A British study found that breast cancers could vary in regards to hormone-sensitivity, lymph node status (positive or negative), but if the tumor tested positive with high levels of Ki-67, the risk of recurrence was higher than average.

Do I Need The Ki-67 Tumor Marker Test?
If your cancer appears to be aggressive, your doctor may order this test to see if Ki-67 is affecting your tumor growth. Other tests must also be done for hormone receptors, HER2 - neu and metastasis, and these results, along with your Ki-67 Labeling Index (test score) will affect your treatment plan.

Benefits of The Ki-67 Tumor Marker Test
A breast tumor that scores high for Ki-67 is made of cells that are rapidly dividing and growing. Chemotherapy drugs target cells that are growing beyond the normal rate, and so these drugs can be effective on aggressive cancers. Knowing your Ki-67 score helps you and your doctor decide what treatment will work best for you.

Balancing Prognosis With Your Response to Treatment
A study in the Journal of Clinical Oncology found that tumors that had higher levels of Ki-67 had a good response to chemotherapy. This study noted that a high index of Ki-67 usually means a poor prognosis (shorter survival), but if the cancer responds particularly well to appropriate chemotherapy, long-term survival is achievable. They also speculate that if the Ki-67 test were done according to consistent standards, the results of a Ki-67 test might be helpful in determining whether or not neoadjuvant chemotherapy (given before surgery) would be effective for some tumors.

Ki-67 and Other Cancers
Ki-67 is found in several types of cancer, some of which are breast, bladder, brain, colon, and prostate cancer.

Sources:

Ki-67 as prognostic marker in early breast cancer: a meta-analysis of published studies involving 12,155 patients. British Journal of Cancer (2007) 96, 1504-1513. E de Azambuja, et. al. Published online April 17, 2007.

Proliferation Marker Ki-67 in Early Breast Cancer. Journal of Clinical Oncology, Vol 23, No 28 (October 1), 2005: pp. 7212-7220. Ander Urruticoechea, Ian E. Smith, Mitch Dowsett.

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