Breast Cancer Ploidy and Cell Proliferation

Finding out more information about the DNA in breast cancer cells can help predict how fast those cancer cells are dividing and growing. If you want to learn more about DNA and breast cancer, you should first understand two important terms: ploidy and cell proliferation.

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 also 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 its 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 proliferation can be estimated by doing a Ki-67 test. In some cases, Ki-67 testing to measure cell proliferation may be used to help plan treatment or estimate treatment outcomes. But test results can vary depending on things like the lab doing the testing, the testing method, and what part of the tumor is tested. 

Another way to determine cell division is the S-phase fraction, which is the percentage of cells in a sample that are copying their DNA as it gets 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.