Researchers from Boston University analyzed data from more than 54,000 black women who were cancer-free at the start of the study. During the next 18 years, 914 women were diagnosed with estrogen receptor positive (ER+) breast cancer and 468 with estrogen receptor negative (ER-) breast cancer.
Women with type 2 diabetes were 43 percent more likely to have developed ER- breast cancer, but had no increased risk for ER+ breast cancer. The study found that the increased risk for ER- cancer was not attributable to their weight.
"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 estrogen receptor negative breast cancer, a more aggressive type of breast cancer which is twice as common in U.S. black women as in white women," said corresponding author Julie Palmer in a university news release.
She's a professor of epidemiology at the university's School of Public Health.
Possible reasons for the increased risk of ER- breast cancer in black women with diabetes include chronic diabetes-related inflammation that can trigger cancer, Palmer suggested.
"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," said Palmer.
But this study only found an association between diabetes and breast cancer, rather than a cause-and-effect link.
The findings were published Nov. 15 in the journal Cancer Research.
SOURCE: Boston University, news release, Nov. 15, 2017
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