Melissa Davis, PhD, Scientific Director of the International Center for the Study of Breast Cancer Subtypes talks about how triple-negative breast cancer is more prominent in African American women.
Can you give some background on the racial disparity in breast cancer?
Davis: Breast cancer doesn’t discriminate in the sense that we’re all vulnerable to our environment, to our inherited genetics, our predisposition to breast cancer. The disparities that we see currently actually exist as a mortality. It’s not necessarily a disparity in the incidence of breast cancer, meaning black and white women. Historically, white women get breast cancer more frequently than black women. But now, those numbers have converged. Whether or not you get breast cancer isn’t the disparity. The disparity is whether you survive it. The mortality disparity is relatively new. In the mid 80s, we started to see an emergence of mortality differences between whites and blacks. Part of that we believe is because treatment got better for certain types of breast cancer. In the last couple of decades, we really didn’t appreciate that there were different types of breast cancer. Surgeons, medical oncologists will certainly be able to say this tumor looks different or it’s not responding the same to chemo. But now we have several molecular markers that allow us to distinguish the actual biological differences between tumor types. What we see across the population when we divide by race is that women of different genetic ancestry tend to get certain biological types of tumors more than others. In the case of African Americans, when a black woman gets breast cancer, most likely, the type of cancer she’ll have is triple-negative breast cancer.
Triple-negative. When you hear that term, what has happened?
Davis: Triple – meaning three. Negative – meaning absent. When a woman is diagnosed with breast cancer, we must assess whether her tumor is expressing estrogen receptor, progesterone receptor or another growth factor receptor called HER-2. Whether she has expression of those three hormone markers on her tumor will dictate what her therapy is going to be. With it being a triple-negative, it just simply means that the tumor does not express any of those markers which, again, feeds into the disparity that we saw. The treatments that have emerged are targeted therapies that target specifically an estrogen pathway or the estrogen receptor or the HER-2 receptor. These are very effective treatments. If you have a type of tumor, and you catch it early enough that it expresses these types of hormone receptors, then the therapies are very effective. When we see white women getting better survival that’s basically how the mortality emerged that white women were dying less than black women. Just died the same amount that they’ve always died from it. The mortality was basically how the disparity formed. What’s interesting though about triple-negative breast cancer is that when you name something by the absence of targetable markers, then it’s not really telling you a lot about what it is. That’s a lot of what our research is about, trying to further define and characterize what triple-negative breast cancer is.
Are there fewer treatments if a woman Is diagnosed with triple-negative breast cancer and what are the options?
Davis: There is an arsenal of drugs that a medical oncologist would use. Of course, there are surgical procedures as well that can help you prolong life. But by and large there are more systemic therapies that just target cancer cells and divide the cells so think of chemotherapy, radiation. There are also several trials now that are using immunotherapies for instance. There are some that have emerged as a first line type of targeted therapy but nothing as good as knowing that the tumor is growing because of, for instance, estrogen and then depriving it of estrogen so that it would literally shrink. That’s how effective targeted therapies are for hormone sensitive tumors. We want to find out what is driving triple-negative tumors. We know it’s not hormones. We know it’s not the estrogen receptors or estrogen. We know it’s not the growth factor. To some extent, we know it’s not other steroid hormones as well because we subtype for other hormone receptors as well. We’re still on the trail of trying to figure out what’s driving the growth because it’s very aggressive, too. The triple-negative breast cancer subtype is a fast-growing version of a tumor. Positive tumors are slower growing. But triple- negatives are aggressive. They become metastatic faster as well.
In addition to hormones, are there other factors at play that work into this racial disparity?
Davis: Part of our work with the International Center looks at the global incidence of breast cancer. For instance, the fact that we see this subtype of breast cancer as the most prevalent form of triple-negative in African Americans, then that begs the question – what is it about African Americans that makes their tumors triple-negative? When we look across the globe, what we see is that women of African descent no matter where they are from, the United States, Europe, Brazil, South America, Africa get a higher incidence of triple-negative breast cancer. European black women get triple-negative breast cancer at a higher rate than white Europeans. All the shared commonality of being African or having some degree of African ancestry is a major flag and clue that there must be a genetic predisposition. Therefore, if it is a predisposition, then there’s a biological mechanism that’s driving it, right? One of the genes that we’re interested in is a chemical receptor. We think it has something to do with an evolutionary shared genetic ancestry that somehow creates this microenvironment that feeds a triple- negative tumor. We’re working hard to try to figure out what those signals are.
When you, your colleagues and researchers can pinpoint what’s driving it, what’s the next step?
Davis: Targeted therapies. If we can identify like luminal breast cancers or ER positive, we can identify what it is that’s driving the aggressiveness. We can try to block it. I believe the next step would be to try to create a specific therapy that is beneficial for people who have this type of breast cancer. We know more about triple-negatives in that we know there’s at least four different subtypes of triple-negatives. It gets more complicated, but this is sort of the avenue of precision medicine as we start identifying with better accuracy. If you know what is driving individual tumors to grow, then we can start designing treatments that target those pathways.
What is the best defense for black women?
Davis: Screening. Early detection is the key to surviving cancer period. We need to do a better job of self-screening. What’s interesting about triple-negative breast cancer and especially in African American women is that it’s early onset, meaning sometimes you know there’s a significant proportion of women who get diagnosed at a premenopausal age and even within the range before mammography screening has been recommended. We must be vigilant as individual women and not wait for the guidelines but be very aware of our environment, our physical activity, the things we eat, our diet, our physical exercise. There’s a list of things. Obesity is one that triggers breast cancer. We know that there is some lifestyle, cultural, environmental factors that increase risk of getting cancer. What I would tell black women is that it’s even more important that you pay attention to what you eat and how you live. Make sure you screen and pay attention to small changes. And let your doctor know so we can be frontline as soon as possible.
Can you talk about the age of onset and how much higher the mortality percentage is from triple-negative?
Davis: Right now, the disparity across the U.S. is about 40% so it’s a 40% difference in the mortality rate. We can’t necessarily say that same disparity exists between blacks and whites within a subtype. For instance, if you have triple -negative breast cancer, whether you’re white or black, you have a lower survival rate. And that five-year survival is probably at least 30% lower with people who have triple-negative.
What percentage of women are in that premenopausal or prescreening early onset guidelines?
Davis: It’s a low percentage. I would say less than 30%. It’s not enough to change the policy because the age group doesn’t have the same risk as the postmenopausal or beyond 40, therefore the guidelines haven’t really changed.
Is there anything else you want people to know or takeaway from this?
Davis: I’d like everyone to know that the ability for us to look at genetics in a population specific way means we’re working to ensure that this is a new era of precision medicine. Generalizable treatments are now sort of becoming more tailored to a specific type of disease or a specific type of person. We have hope that these mortality rates will start to get lower. There will no longer be a difference, but we’ll certainly have to address equity. For the black population they do tend to have less access to treatment. This is also part of the reason why their mortality is higher. But for those who do have access and get detected early, we still need better treatment options. Once we deal with the equity issue, they should have the right treatment no matter what. Part of that means we need to include a bigger diversity of ethnic groups so that we can really capture the variety of diseases that occur in the breast tumor.
Interview conducted by Ivanhoe Broadcast News.
END OF INTERVIEW
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