Breast Cancer Ploidy and Cell Proliferation

By learning about how fast cancer cells are growing and dividing, the aggressiveness of the cancer can be assessed. Ploidy refers to the amount of DNA in cells. Diploid cancer cells have a normal amount of DNA and tend to grow and spread more slowly, while aneuploid have an abnormal amount of DNA and tend to grow and spread more quickly. Tests of ploidy are not usually part of a routine breast cancer work-up because they rarely affect which treatments are chosen, but they can be useful in assessing long-term outcomes.[1]

Cell proliferation can be measured to determine how fast cells are dividing. The rate of cell proliferation can be determined with a Ki-67 test.1 Ki-67 is a protein present in proliferating cells; therefore, the amount of the protein present in cancer cells is used as an indicator for how aggressive the cancer is.[2] A high Ki-67 test result means that the cancer cells are dividing rapidly, and the cancer is more aggressive.1 Ki-67 test results are given as a percentage, and a result of less than 10% is considered low, greater than 20% is considered high, and between 10-20% is considered borderline.[3]

These tests results are sometimes used to help plan treatments or predict treatment outcomes. Since chemotherapy targets rapidly dividing cells, cancers with high Ki-67 levels tend to respond well to chemotherapy. Ki-67 test results are used when classifying breast cancers by molecular subtype. The two hormone receptor-positive subtypes, luminal A and luminal B, are differentiated by Ki-67 levels. Luminal A breast tumors have low Ki-67 levels, while luminal B breast tumors have high Ki-67 levels.[2] The S-phase fraction can also be used to measure cell proliferation by determining the percentage of cells in a sample that are in the S phase of the cell cycle meaning they are in the process of copying their DNA.[1] A S-phase fraction less than 6% is considered low, greater than 10% is considered high, and between 6-10% is considered intermediate.[3]

References

1.     Breast Cancer Cell Proliferation and Ploidy https://www.cancer.org/cancer/breast-cancer/understanding-a-breast-cancer-diagnosis/ploidy-and-cell-proliferation.html (accessed Jun 24, 2021).

2.     Stephan, P. The Ki-67 Proliferation Marker Test and Breast Cancer Treatment https://www.verywellhealth.com/ki-67-tumor-marker-test-430609#:~:text=The%20Ki-67%20test%20may%20be%20performed%20on%20a,in%20the%20cancer%20cells%20through%20a%20staining%20process. (accessed Jun 24, 2021).

3.     Rate of Cell Growth https://www.breastcancer.org/symptoms/diagnosis/rate_grade#:~:text=S-phase%20fraction%3A%20This%20number%20tells%20you%20what%20percentage,intermediate%2C%20and%20more%20than%2010%25%20is%20considered%20high. (accessed Jun 24, 2021).