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

Understanding Tumor Aggressiveness and Predicitng Prognosis

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What is the Ki-67 tumor marker test for breast cancer, when is it done, and what does it mean with regard to treatment and prognosis?

Ki-67 Tumor Marker - Definition

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.

About the Ki-67 Tumor Marker and Breast Cancer

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. Researchers agree that high levels of Ki-67 may indicate an aggressive tumor and predict a poor prognosis. Regardless of hormone sensitivity or lymph node status, tumors with high levels of Ki-67 appear to be more likely to recur and have a poorer prognosis. If your level of Ki-67 came back negative, it's not yet time for alarm.  It may just be that your tumor should be treated more aggressively that if you did not have a tumor with an elevated Ki-67.

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 Biomarker 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 treatments will work best for you.

Balancing Prognosis With Your Response to Treatment

Studies have found that tumors with higher levels of Ki-67 have a poor prognosis, but also, respond particularly well to chemotherapy.  This was the case whether or not people had positive lymph nodes on their initial diagnosis.  There is still considerable controversy over the value of this test, but it may be helpful in determining whether or not adjuvant chemotherapy should be used for tumors where it would not otherwise be recommended - for example, small, node-negative 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.

Coping with an Abnormal Test Result

Knowing that the Ki-67 tumor marker may give evidence about prognosis, you may be feeling very anxious if your level is abnormal.  It's important to know the treatments, even for the most advanced breast cancers, are improving every year.  Reach out to your family, and consider connecting with a support group in your community, or an online breast cancer community.

  These groups not only lend support but are a great place to gain information and understanding of your disease. There is a lot of reason for hope.


de Azambuja, E., Cardosa, F., de Castrok, G. et al. 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.

Kontzoglou, K., Palla, V., Karaolanis, G. et al. Correlation between Ki67 and breast cancer prognosis. Oncology. 2013. 84(4):219-25.

Luporsi, E., Andre, F., Spyratos, F. et al. Ki-67: level of evidence and methodological considerations for its role in the clinical management of breast cancer: analytical and critical review. Breast Cancer Research and Treatment. 2012. 132(3):895-915.

Perez-Lopez, M., Garcia-Gomez, J., Alves, M. et al. Ki-67 is a prognostic marker for hormone receptor positive tumors. Clinical & Translational Oncology. 2016 Jan 7. (Epub ahead of print).

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