Sociogenomics may explain race disparities in breast cancer mortality



Racial differences in cancer outcomes are widespread. Studies indicate that Black people face higher rates of mortality for most cancers than their White counterparts. To bridge this racial gap, researchers need to investigate the biological effects of structural racism and discrimination on cancer outcomes, experts say.

“As a physician, I always like to think that I can influence care in that if I just find the right drugs, help patients understand what their options are, it will help them,” said Ruth Carlos, MD, a radiologist with the University of Michigan Hospital, Ann Arbor. But these things alone are often not enough, because a large proportion of the variation in cancer outcomes is attributable to neighborhood social conditions and the physical environment. “It is incredibly important for us to start to understand just how the neighborhood exerts this effect.”

In a commentary published in the Journal of Clinical Oncology, Dr. Carlos and colleagues highlighted the limitations of previous studies aimed at identifying the causes of racial differences in cancer outcomes. They call upon researchers to turn instead to the long-underexamined biological effects of structural racism and discrimination that contribute to these differences.

In the past, studies on the role of race in health outcomes largely looked at race as a proxy for genetic predisposition. But such an interpretation is flawed, because no genes are specific for a racial or ethnic group, Dr. Carlos and coauthors wrote. Researchers have shown that the vast majority of genetic variation occurs within, rather than between groups.

In an analysis published in Science, researchers reported that within-group differences account for more than 90% of genetic variation.

“Using race in these analyses was not necessarily wrong, but the inferences may have been flawed or incomplete,” Dr. Carlos said. On one hand, looking at genetic predisposition has led to important insights, such as the link between mutations in the BRCA gene and increased risk for breast and ovarian cancer.

However, genetic variation alone is not enough to explain the disparities in cancer outcomes between racial and ethnic groups. The fact that breast cancer can be more aggressive in Black women raises several questions, Dr. Carlos said. Is the cancer worse because Black women have a specific genetic predisposition? Is it worse because Black women exist in a society that marginalizes them and exposes them to increased stress, which in turn produces bad outcomes? Or, could it be both?

Despite progress in the screening, diagnosis and treatment of breast cancer, Black women are 40% more likely to die from the disease than White women. At the time of diagnosis, Black women are more likely to have high-grade, more aggressive breast cancer molecular subtypes, and to have had their cancer spread to the lymph nodes. They also tend to be diagnosed at more advanced stages of breast cancer while at the same time, experience higher rates of false-positive screening results.

Although researchers have hypothesized that genetic differences related to African or European ancestry might contribute, studies have not turned up any differences in cancer susceptibility genes by race. Other factors, such as racial differences in the stage of presentation, molecular subtypes, and disparities in treatment, have also emerged as potential culprits.

In her commentary, Dr. Carlos and colleagues wrote that disparities in breast cancer outcomes previously attributed to race need to be examined from multiple angles. This means looking at both the complex interactions between social conditions and policies, which encompass racism both at the individual and structural level, and stressors such as the experience of discrimination in addition to potential biological and genetic contributions.

Many studies now provide evidence for the harmful effects of racism on health. For breast cancer, specifically, studies also suggest that factors such as racial segregation can influence the stage at which Black women get diagnosed and their likelihood of dying from the disease.

However, an important question that remains is what biological changes occur in women exposed to the kind of persistent low-level stress that is associated with structural racism and discrimination, Dr. Carlos said. “We don’t know what stress pathways actually manifest in the body and how they eventually produce the disease.” Studies to address this issue are important, “especially if you would like to develop interventions to prevent or mitigate disease.”

To address this issue, Dr. Carlos and colleagues called upon the research community to conduct both studies that delineate the underlying biology as well as those that test potential interventions – particularly those associated with breast cancer screening outcomes – to try to shed light on why Black women receive more false positives and diagnoses of more aggressive cancer.

Interventions that can target these specific biological pathways could potentially reduce the negative effects of structural racism and discrimination as well as the effects of other social factors that contribute to breast cancer outcomes, “to ultimately help enhance clinical outcomes and close persistent disparities gaps,” the authors wrote.

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