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Breast Cancer Outcomes Vary by Ethnicity — a New Study Tackles Why

Breast cancer is the most common type of cancer for women in the U.S., but the exact statistics vary by ethnic group and by breast cancer type.

For instance, the U.S. Centers for Disease Control reports that breast cancer is the leading cause of cancer mortality for Hispanic women, but is the second most common cause for white, black, Asian/Pacific Islander, and Native American women. Professor Jill Bargonetti (Hunter College, The Graduate Center) is unraveling the biological reasons behind these variations by studying proteins involved in the disease.

In a paper published in Breast Cancer Research and Treatment, Bargonetti looked at three different proteins in breast cancer patients of different ethnic groups to determine how they were related to outcomes. These proteins included a mutant version of p53, a protein which normally helps suppress tumors, as well as MDM2 and MDM2-C, two proteins that interact with p53.

The researchers found that the proteins and their roles varied from group to group, just as mortality statistics do. For example, they saw a correlation between the presence of MDM2-C and a reduced risk of breast cancer mortality in white patients. But this trend did not show up for the other groups, including Japanese and Native Hawaiian patients. This could mean the proteins’ roles are not always clear cut—MDM2-C could be ‘good’ or ‘bad’ depending on whether mutant p53 is also present.

In another paper published in Breast Cancer Research, Bargonetti and collaborators asked what effects these proteins have in different subtypes of breast cancer. In triple-negative breast cancer, the researchers found, a protein called MDMX contributes to metastasis, something MDM2 is also known to do. Metastasis is when a cancer travels from the original tumor to a new part of the body. Metastatic breast cancer is currently untreatable, but these findings suggest that researchers could look into targeting MDMX to prevent metastasis from happening in the first place.

In another kind of breast cancer, called estrogen receptor alpha-positive, the authors saw that MDM2 promotes tumor growth. However, MDM2 works in a different way in this kind of cancer than it does in triple-negative breast cancer.

Differences like this could be useful for clarifying the differences of breast cancer subtypes, the authors say.