Breast Cancer: Ploidy and Cell Proliferation

These tests provide information about the DNA in the breast cancer cells, and can be used to help predict how fast the cancer cells are dividing and growing.

What is ploidy and what does it mean?

The ploidy of cancer cells refers to the amount of DNA they contain.

  • If there's a normal amount of DNA in the cells, they are said to be diploid. These cancers tend to grow and spread more slowly.
  • If the amount of DNA is abnormal, then the cells are called aneuploid. These cancers tend to be more aggressive. (They tend to grow and spread faster.)

Tests of ploidy may help figure out long-term outcomes, but they rarely change treatment and are considered optional. They are not usually recommended as part of a routine breast cancer work-up.

 What is cell proliferation?

Cell proliferation is how quickly a cancer cell copies it’s DNA and divides into 2 cells. If the cancer cells are dividing more rapidly, it means the cancer is faster growing or more aggressive.

The rate of cancer cell division can be estimated by doing a Ki-67 test. The S-phase fraction is the percentage of cells in a sample that are copying their DNA. DNA is copied when the cell is getting ready to divide into 2 new cells. If the S-phase fraction or Ki-67 labeling index is high, it means that the cancer cells are dividing more rapidly.

 In some cases, Ki-67 testing to measure cell proliferation may be used to help to plan treatment or estimate treatment outcomes. But test results vary depending on things like the lab doing the testing, the testing method, and what part of the tumor is tested. Still, there’s a lot of interest in measuring tumor proliferation and standardizing testing methods, so this test is being used more often.

Questions to ask your doctor

These are some questions that would be good to have on hand when talking to your doctor about your breast cancer test results:

  • Will ploidy and/or cell proliferation tests be done on my cancer?
  • If so, what do my test results mean?
  • How will they affect my treatment plan?

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

American Society of Clinical Oncology. Breast Cancer in Men: Diagnosis. 08/2014. Accessed at on September 25, 2015.

Last Medical Review: June 1, 2016 Last Revised: August 18, 2016

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