Study Finds Genomic Differences Between Breast Cancers in Black and White Women

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Historically, black women have been more likely to be diagnosed with breast cancer when they were younger than 40 and more likely to die from breast cancer than white women. Black women also are more likely to be diagnosed with triple-negative breast cancer. Triple-negative breast cancer has no receptors for the hormones estrogen or progesterone and also has no HER2 receptors. This limits the treatments that can be used. Triple-negative breast cancer is considered more aggressive than hormone-receptor-positive disease.

For many years, black women also were less likely overall to be diagnosed with breast cancer than white women. But an October 2015 report from the American Cancer Society found that for the first time, rates of breast cancer among black and white women were about equal.

Now another study has found genomic differences in breast cancers in black women compared to breast cancers in white women. These genomic differences may help explain why breast cancer is more aggressive in black women.

The study was published online on Sept. 14, 2015 by the Journal of Clinical Oncology. Read the abstract of “Comparison of the Genomic Landscape Between Primary Breast Cancer in African American Versus White Women and the Association of Racial Differences With Tumor Recurrence.”

A genome is the complete set of DNA (deoxyribonucleic acid) of a living thing, including all of its genes. Genes are made up of DNA. DNA can change or be damaged over time. Some DNA changes, also called mutations, are harmless, but others can cause disease, such as breast cancer.

As researchers work to find more effective treatments for breast cancer, they have started analyzing (or sequencing) the genomes of cancers to see the types of mutations in them.

In this study, the researchers analyzed the genomes of breast cancer diagnosed in black women (105 women) and white women (664 women) between 1988 and 2013. The genomes were part of the National Cancer Institute’s Cancer Genome Atlas.

The analysis showed that five mutations were prevalent among the breast tumors of both black and white women. Still, the tumors of black women were more likely to have a mutation in the TP53 gene (also called p53). In breast cancer tumors, a TP53 mutation means that the tumor is likely to be more aggressive. The tumors of white women were more likely to have a PIK3CA mutation. In breast cancer tumors, PIK3CA mutations means the tumor is more likely to be hormone-receptor-positive, which is considered a less aggressive breast cancer subtype.

The researchers also found that there were more mutations within each tumor removed from black women compared to the number of mutations in tumors removed from white women. Tumors with more mutations are considered more aggressive.

The tumors of black women also had more basal-like cells compared to the tumors of white women. This means that the cells resemble the basal cells that line the breast ducts. Basal-like cancers tend to be more aggressive and higher grade. It’s believed that most triple-negative breast cancers are made up of basal-like cells.

Breast cancer tumors were more likely to recur (come back) and recur more quickly in black women, especially tumors with basal-like cells or tumors that had a TP53 mutation.

“We found that African American women with breast cancer had a significantly higher prevalence of the TP53 driver mutation, basal tumor subtype, and greater genomic diversity within tumors, all of which suggest more aggressive tumor biology," said Tanya Keenan, M.D. of the Massachusetts General Hospital Cancer Center and lead author of the study. "The higher risk of tumor recurrence that we observed among African American women was reduced when controlling for those factors, suggesting that these genomic differences contribute, at least partly, to the known racial disparity in the survival of African American and Caucasian breast cancer patients."

The researchers said that if their findings are confirmed by other studies, the work may lead to the development of targeted therapies aimed at the tumor subtypes more likely to affect black women.

We know you can’t change your genetics. Still, there are steps that women of all ethnicities can take to keep their risk of breast cancer as low as it can be, including:

  • maintaining a healthy weight
  • exercising every day
  • limiting or avoiding alcohol
  • not smoking
  • eating a healthy diet that’s low in processed foods, sugar, and trans fats

To learn more about breast cancer risk and other options to keep your risk as low as it can be, visit the Breastcancer.org Lower Your Risk section.

And stay tuned to Breastcancer.org Research News for the latest information on targeted therapies and other new breast cancer treatments.



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