In recent years, a crop of scientific studies has shown the racial disparity that exists when diagnosing and treating various diseases, in particular, cancer. While some studies found that the inequality was rooted in racial and social bias for disease diagnosis, others have found the genetics associated with various racial backgrounds has a profound influence on disease risk. The latter scenario is exactly what investigators from Boston University found after the results from their recent study showed that African American women with type 2 diabetes (often referred to as adult-onset diabetes) are at a greater risk for developing estrogen receptor-negative (ER) breast cancer.       

Findings from the new study were released today in Cancer Research in an article entitled “Type II Diabetes and Incidence of Estrogen Receptor Negative Breast Cancer in African American Women.” The research was based on data of 54,337 African American women enrolled in Boston University's Black Women's Health Study (BWHS) who were cancer free at enrollment in the study in 1995 and were followed for up to 18 years. During follow-up, 914 ER+ cases and 468 ER cases were identified.

Evidence has emerged in recent years that the two major subtypes of breast cancer—ER+ and  ER  breast cancer—differ in some cases. Thus, the investigators focused on whether type 2 diabetes had differing associations with ER+ and ER cancer.


“We are still trying to understand the basic biological processes that lead to ERbreast cancer,” explained lead study investigator Julie Palmer, Sc.D., associate director of Boston University's Slone Epidemiology Center, professor of epidemiology at Boston University School of Public Health, and associate director for population sciences at the BU-BMC Cancer Center. “One way to do this is to study factors that are more common in an African American population.”

African American women with type 2 diabetes were estimated to have a 43% increase in the risk of ER breast cancer relative to women without diabetes; in contrast, there was no increase in the risk of ER+ breast cancer among women with diabetes relative to women without diabetes. The increased risk of ER breast cancer among women with diabetes was not explained by obesity status.

“Our results showed statistically significant evidence of an increased risk of ER breast cancer in black women who had type 2 diabetes before they ever had breast cancer, primarily in the women who had diabetes for at least five years,” Dr. Palmer noted. “While we observed no association for the most common type of breast cancer, the type that is responsive to estrogens, women with diabetes were estimated to be at increased risk of developing ER breast cancer, a more aggressive type of breast cancer that is twice as common in U.S. black women as in white women.”

Several studies suggest that diabetes is a risk factor for breast cancer, and type 2 diabetes is twice as prevalent in African American women as compared to white women. One previous study analyzed the association between type 2 diabetes and breast cancer in African American women but did not report results separately for ER and ER+ breast cancer.

For the current analysis, Dr. Palmer and her colleagues compiled information provided by participants in the BWHS. The BWHS was established over 20 years ago and utilizes biennial questionnaires to obtain information from 59,000 African American women from across the United States. Using this large dataset, the research team could control for many factors, including age and body mass index (BMI).

“Our findings may account for some of the racial disparity in breast cancer, and could partly explain why mortality from breast cancer is so much higher in black women than white women,” Dr. Palmer remarked. She stressed that further work is needed to corroborate these relatively new findings. “If these results are confirmed, type 2 diabetes would be a modifiable risk factor for ER breast cancer. Women could reduce their chances of getting ER breast cancer if they could avoid developing type 2 diabetes. Monitoring of blood sugar levels to identify prediabetes may allow for early interventions to prevent diabetes.”

The research team hypothesized that an explanation for an increased risk of ER breast cancer among women with diabetes includes chronic inflammation resulting from diabetes that, among other actions, can promote carcinogenic processes.

“Given that the prevalence of diabetes is twice as high in African Americans as in whites, the current finding, if confirmed, may help to explain the higher incidence of ER breast cancer in African American women,” Dr. Palmer concluded.

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