Women of color and younger women have higher relative odds of developing aggressive triple-negative breast cancer (TNBC), according to findings from a study that included data on more than a million women with cancer held in the United States Cancer Statistics (USCS) database. The new study, involving women across the U.S., supports smaller-scale, and largely state-restricted studies that have previously pointed to racial disparities in TNBC.
TNBC has a poor prognosis, and doesn’t respond to hormone therapy or targeted treatments, so it is important to understand which individuals are at a relatively higher risk of developing the disease, and why, noted research lead Lia Scott PhD, MPH, at Georgia State University School of Public Health. “With the advent and availability of more comprehensive cancer data, such as the United States Cancer Statistics database, it is important that we continue to explore disparities in order to better inform practice and policy around screenable cancers like breast cancer. We hope that this update on the epidemiology of triple-negative breast cancer can provide a basis to further explore contributing factors in future research.”
Scott and colleagues report their findings today in Cancer, in a paper titled, “Update on Triple-Negative Breast Cancer Disparities for the United States: A Population-Based Study from the United States Cancer Statistics Database, 2010 Through 2014.”
Figures suggest that triple-negative breast cancer accounts for approximately 15% of all breast cancer cases, and is associated with aggressive histology, poorer prognosis, and shorter survival. TNBC is also unresponsive to hormone therapy, the authors explained. Prior studies have also indicated that younger women, or those of African-American, and non-Hispanic black (NHB) ethnicity have a higher relative risk of TNBC. Such racial disparities persist even after accounting for known risk factors, particularly between non-Hispanic white (NHW) and NHB populations, the researchers continued. “The focus on TNBC is due to its aggressive nature and poor prognosis, and therefore it is imperative to continue identifying risk factors, whether environmental or genetic, that exacerbate disparities in breast cancer diagnosis to develop and implement more efficacious population-based prevention strategies.”
Scott et al., evaluated TNBC cases put into the USCS database between 2010 and 2014, including women across 39 states for which there was complete data. The USCS database is a population-based surveillance system of cancer registries with data representing approximately 99% of the U.S. population, which combines data from both the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) program, and the Centers for Disease Control and Prevention’s National Program of Cancer Registries. The researches evaluated cases between 2010 and 2014, because UCSC didn’t start collecting data on human epidermal growth factor receptor 2 (HER2) status until 2010.
The resulting dataset included 1,151,724 breast cancer cases in the 39 states, with a mean age at diagnosis of 61.8 years. Approximately 75% of all cases were NHW women. Over the time period covered, TNBC cases accounted for 8.4% of all breast cancer cases. This finding is somewhat at odds with those of prior studies, which indicated that TNBC might account for some 15% of all breast cancer cases. “The lower incidence of TNBC potentially could be due to changes in data collection from registries because 2010 was the first year that SEER began collecting data regarding HER2 status for breast cancer cases,” the investigators pointed out.
Compared with NHW women, NHB, Hispanic, and American Indian/Alsaka Native women were at increased risk of TNBC, whereas Asian women and those of other ethnicities had lower odds of a TNBC diagnosis. “NHB women accounted for a larger percentage of TNBC cases, 21.4%, compared to overall breast cancer cases, 10.9%,” the team reported. “After controlling for late-stage diagnosis and case age, NHB women had approximately twice the odds of diagnosis with TNBC compared with NHW women, whereas Hispanic women had odds of a TNBC diagnosis that were similar to those of NHW women.”
More specifically, the results showed that compared with non-Hispanic white women, NHB women and Hispanic women had 2.3-times and 1.2-times higher odds, respectively, of being diagnosed with triple-negative breast cancer. More than 21% of NHB women were diagnosed with TNBC, compared with less than 11% for all other types of breast cancer. Women younger than 40 years of age had twice the odds of a TNBC diagnosis than women aged 50–64 years. And among women who were diagnosed with breast cancer, those diagnosed at late stages were 69% more likely to have triple-negative cancer than other types.
The researchers say that to their knowledge, their study represents the most geographically broad with respect to the U.S. states included, and the most recent, in terms of data examined. “Using more current data ensures the consistency of TNBC coding and provides an improved estimate of the overall burden of this highly problematic type of breast cancer,” they stated. “Having a broader sample brings greater heterogeneity in terms of local context into the realm of analysis, which can be fruitful when using variations across predictors to explain variations across geography in future studies.”
The data confirm the racial disparities in TNBC that have been reported previously, “and demonstrated that, with regard to the diagnosis of TNBC, there are significant burdens among women of color, specifically NHB women; younger women; and women diagnosed at a later stage.”
The investigators note that by focusing on TNBC the study was limited in scope, so future studies might expand that scope and look at different subtypes of breast cancer, and also include additional information on disease stage, as the reported work focused on diagnosis at latter stages. “Additional studies are needed to determine drivers of disparities between race, age, and stage of disease at diagnosis,” they wrote.
