New research has revealed significant molecular differences between the breast cells of white and Black women that help explain why Black women are much more likely to die of breast cancer.
The findings, published on February 8 in the journal Therapeutic Advances in Medical Oncology, suggest that changing current diagnosis and treatment strategies could help address the disparity – and improve mortality rates for Black women.
Studies show that while Black women are less likely to develop breast cancer than white women, they are far more likely to be diagnosed at a late stage and to die from the disease.
Scientists at Sanford Burnham Prebys found there were significant differences between white and Black women in the way DNA repair genes are expressed, both in healthy breast tissue and in cancerous tumors.
These molecular differences also corresponded with changes in how quickly cancer cells in the breast can grow.
‘What we’re seeing here is a tangible molecular difference in how these cells repair damaged DNA – a critical factor in the development of cancer – which affects how cells grow and reproduce in tumors,’ says Svasti Haricharan, Ph.D. an assistant professor at Sanford Burnham Prebys.
‘The way each human being responds to cancer treatment is influenced by so many internal and external factors that are unique to each of us.
‘The scientific community has to confront this and invest time and money into understanding it, because everybody deserves care that is tailored to their molecular makeup as closely as possible.’
What did the study find?
Put simply, researchers found that Black women’s cells repair DNA differently to white women’s cells – which means they will respond differently to certain cancer treatments.
DNA repair is a fundamental part of normal cell function, regulating processes throughout the cell and helping them recover from errors that occur naturally during DNA replication, or in response to external factors like stress.
Unlike healthy cells, cancer cells often acquire genetic changes that make it impossible for them to repair DNA, which can then make these cells resistant to treatment.
‘We have already seen how defects in DNA repair lead to treatment resistance in breast cancer. But until now, there weren’t studies to measure the degree to which this differs in Black versus white women or what’s driving that difference,’ Svasti says.
To fill this gap, Svasti and her team looked at both healthy and tumour tissue from 185 Black women and compared these to samples from white women.
They found that eight genes powering DNA repair are expressed differently in Black women.
The difference in DNA repair pathways
‘Black women who get ER+ breast cancer, which is considered the “easier” form of breast cancer because we know how to treat it, have much worse outcomes than white women. However, when they get more aggressive forms of breast cancer, Black women have similar outcomes to white women.
‘We found that there was a completely different set of of DNA damage repair genes and the activity was different in Black women. What it was essentially doing, was creating these tumours that are completely resistant to standard care.
‘So even though the tumours look like the tumours we see in white women, because of the change in DNA damage repair activity, there is a difference there that stems even from normal breast cells in Black women. It is just a different way of regulating your DNA repair pathways.’
Svasti Haricharan, Ph.D., assistant professor at Sanford Burnham Prebys
They also found consistent molecular differences in the signals controlling how fast cells can grow. Notably, these differences were not confined to cancer cells – even healthy tissue showed a different gene expression pattern in Black versus white women.
‘This is so important because if the normal tissue is different at the molecular level based on race or ethnicity, then everything we understand about how each of us responds to cancer treatment is going to be different as well,’ Svasti adds.
Why this doesn’t mean race has a genetic basis
The idea that your DNA can be being impacted by your race steers dangerously close to concepts of race science – which have historically been used to justify abhorrent and unequal treatment of Black people in medicine and beyond.
However, the scientists involved in this study are keen to reiterate that these findings don’t contradict the claim that race is a social construct.
Svasti wants to make it very clear that this study was not about ancestral differences – or genetic distinctions that indicate any kind of innate, biological difference between racial categories.
‘My biggest worry with this study is that it will be misunderstood. None of the results we found have anything to do with ancestry,’ Svasti tells Metro.co.uk.
‘Ancestry is about the DNA that we are born with – that isn’t what we have looked at here. The DNA and molecular pathways that we studied could very easily be affected by lifestyle, climate conditions, systemic racism in healthcare.
‘The pathways we looked at are some of the most volatile pathways. They are made to respond to what is happening outside the person, to external threats from the environment that are damaging the DNA and causing stress. They respond to that by changing how they are regulated.’
She says the reason behind Black women having different DNA to white women could still be caused by social factors – such as socioeconomic inequality and racism. She says the outside world inevitably has a deep impact on our bodies.
‘We think these findings could very well be a reflection of socioeconomic status,’ she says.
‘Our contention is that in the field of cancer research – especially cancer research disparities – there aren’t two separate camps of external or internal causes.
‘To suggest that there isn’t a link between what’s happening outside your body and what’s happening inside it, is crazy. we know there’s a link. Our lived experiences can change the molecular biology of our cells.
‘What matters to me is that there is an actionable difference, consistent across different datasets. Why aren’t we taking that on board?
‘There is no current clinical diagnostic that predicts response to therapy for breast cancer patients that’s not based on data from white people. All of our treatment and diagnostic options are tailored to what we know happens with white patients, but you can’t have precision medicine if you’re only being precise for one demographic. What happens to everyone else?’
Black women with breast cancer: Worse outcomes, less research
Black people have the highest cancer mortality rate of any racial or ethnic group.
Among Black women, breast cancer makes up about a third of all cancer diagnoses, with the breast cancer being the most common. According to the scientists at Sanford Burnham Prebys, Black women with the most common forms of breast cancer are 42% more likely to die of the disease than white women, and while there are lifestyle and socioeconomic factors that contribute to this disparity, such as access to healthcare, researchers say they are not enough to fully account for the difference.
‘Society has internalised the narrative that lifestyle factors are to blame for racial differences in health outcomes, so most scientists don’t look at molecule-level differences between people,’ says Svasti.
‘It also makes people who are sick feel they are somehow at fault because of how they’re living their lives. Now we’re seeing that it’s so much more complicated than that.’
One barrier to fully exploring the disparities between white and Black women with breast cancer is the historical lack of data on non-white patients.
‘Black women are severely underrepresented in virtually all datasets of patient tumors, so a lot of previous results about breast cancer only accurately reflect what’s happening to white women,’ adds Svasti.
‘We hope our research will highlight the need to study cancer in different racial and ethnic groups more closely and improve outcomes for historically marginalised patients.’
What do the findings mean for breast cancer patients?
The good news, according to this research team, is that the findings suggest a change in our approach to treating breast cancer in Black women could significantly improve outcomes.
The scientists found that treatments that already exist will work better for Black women in light of this new knowledge – but doctors may have to give Black patients different drugs to white patients.
‘What’s really interesting is that the different DNA repair process in Black women makes the tumours actually really sensitive to a different therapy – one that is actually approved for breast cancer patients, but is typically only given when the patient relapses.
‘This was the biggest take-home for us. It’s not just that there are differences, but these are differences that we can actually act on.
‘If we give Black patients that FDA approved therapy earlier, it would probably improve their outcomes.
‘At the moment, we are treating Black women in the same way we treat white women, even though the molecular pathways are different – which means we are exposing them to worse outcomes, which is something that is completely preventable in my opinion.’
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