Racial and ethnic disparities in breast cancer
Experts gain new clues about differences in mortality rates among racial groups
Although racial and ethnic disparities in cancer outcomes continue to persist, scientists are gaining new insights into potential causes and solutions. “African American women continue to have higher breast cancer mortality than white women even in clinical trials where all the patients are receiving the same treatment,” says Christine Ambrosone, PhD, chair of the department of cancer prevention and control at the Roswell Park Cancer Institute in Buffalo, New York.
In the past, disparity experts have assumed that when compared with white women, African American women were generally diagnosed at a later stage of the disease, did not receive the same treatment, or had factors making it difficult for them to comply with treatment, all of which contributed to their higher mortality rates. However, Dr. Ambrosone says that additional factors may come into play.
She and others have started to glean additional clues about these disparities as scientists learn more about different subtypes of breast cancer, who is more likely to have them, and how these individuals are treated. Treatments that help to extend survival have been developed for patients with both estrogen receptorpositive (ER+) and human epidermal growth factor receptor-2 (HER2)/neu-positive breast cancers. Another subtype, the luminal A (ER+ and HER2/neu-negative) subtype, has the best prognosis and is more common among older white women.
Basal-like breast cancers are high-grade, “triple-negative” tumors that do not express ER, progesterone receptor (PR), or HER2/neu proteins. They are more aggressive cancers and tend to have a poorer prognosis. These tumors also are twice as common in African American women and much more common in young women, Dr. Ambrosone says, adding that these findings have opened many new avenues for research focused on how lifestyle factors influence breast cancer risk.
“Anything that extends the period from menarche to menopause is thought to change the architecture of the breast, and we've always said that parity reduces the risk of breast cancer,” she says. “But most of those studies have been done in white women. And we're finding that for basal-like breast cancer, pregnancy actually increases risk.”
However, researchers using data from the Black Women's Health Study led by Boston University in Massachusetts found that breastfeeding nearly eliminated that increased risk. In a 2011 article published in Cancer Epidemiology, Biomarkers and Prevention, investigators reviewed 457 cases of both ER+ and PR-positive (PR+) and triple-negative cancers. Higher parity was found to be associated with an increased risk of triplenegative breast cancer and a lower risk of ER+/PR+ disease; however, among women who had breastfed, parity was no longer associated with an increased risk of triple-negative cancer.
Compared with white women, African American women generally have children at a younger age, have more children, and have a lower rate of breastfeeding. The investigators concluded that the higher incidence of triple-negative breast cancer may be associated with these factors.
More Data Needed
“One reason there hasn't been better understanding of breast cancer in black women is that you need large sample sizes in order to look at specific subtypes,” says Dr. Ambrosone. For that reason, she and her colleagues from the Black Women's Health Study and Carolina Breast Cancer Study decided to collaborate to pool data and tumor tissue in an effort to learn more about these subtypes and risk factors. The effort, which also involves the Women's Circle of Health Study and the Multi-Ethnic Cohort Study, received a program project grant from the National Cancer Institute and is in its third year of funding. Investigators hope that by pooling data, they will be able to learn more about the etiology of aggressive early-onset breast cancers in African American women.
Thus far, their data support previous findings of the relations between breastfeeding and parity and triple-negative breast cancer. “Our hope is that we'll have convincing data that will provide evidence for a greater public health effort to encourage more African American women to breastfeed and also make it easier to breastfeed in the workplace,” Dr. Ambrose says.
She and her colleagues also are investigating another hypothesis regarding low vitamin D levels, which have been associated with more aggressive triple-negative tumors. African American women tend to have much lower levels of vitamin D than white women because of the higher melanin content in darker skin that blocks vitamin D absorption from the sun, says Dr. Ambrosone. “I'm very interested in prevention and understanding the causes of disease so we can intervene,” she says. “Vitamin D supplementation and breastfeeding are easy approaches to reducing risk.”
Richard Wender, MD, who recently was named to the newly created position of chief cancer control officer for the American Cancer Society (ACS), believes that genetic differences that influence cancer development and have been linked to certain racial and ethnic disparities cannot be fully separated from environmental factors. His role with the ACS will be to focus the society's consumer and clinical guidance on cancer prevention and early detection and their implementation through evidencebased cancer control interventions.
“We know that gene expression changes dramatically based on exposures and experiences; even a stressful day changes gene expression,” he says. “What you eat and weigh, how active you are, if you smoke or are exposed to pollution-all of these determine gene expression and risk.”
For that reason, Dr. Wender adds, disparities may not be attributed to race and skin color alone but to exposures and life experiences that different populations are more likely to face. An example supporting that scenario are studies that have been conducted in Scandinavian countries in which everyone has the same skin color but where women who grew up in poverty have higher cancer rates, he says.
In an effort to tackle cancer disparities in his new role at the ACS, Dr. Wender and his colleagues will use data to find pockets of excess cancer mortality, most likely in rural and urban areas with high poverty levels.
“We will target partners and systems that have the potential to improve care; change living environments; and improve access to prevention, early detection, and treatment,” he says, adding that these partners will include policy makers, insurance companies, and community providers that form the safety net of care for at-risk groups.
Education level is the single best predictive factor for ensuring good prevention and treatment, Dr. Wender says. “We need to expand our measures of what health policy is,” he says. “Our housing policy is our health policy. Our policies on how we build healthy communities are part of our health policy.”
Although he considers research into genetic causes of racial differences in cancer important, Dr. Wender also is a strong proponent of research that analyzes multiple socioeconomic factors, which are difficult to separate from race itself. “I think researchers understand that looking at race alone risks missing what really are the more fundamental determinants of the biology of tumors, including where people live and the exposures or lack of exposures they've had in their lives.”