Black women have fewer breast cancers than white women, but their mortality is worse

For decades, researchers have tried to understand why breast cancer in younger black women is such a significant public health problem.

Black women have fewer breast cancers than white women, but their mortality is worse. Black women under the age of 50 have a 77 percent higher mortality rate from breast cancer than white women of the same age.

Results of a study led by scientists from the University of North Carolina at Chapel Hill schools of Public Health and Medicine and the UNC Lineberger Comprehensive Cancer suggest one reason for these differences.

When younger, premenopausal, black women get breast cancer, they are more than twice as likely as older women, black or white, to get an aggressive breast cancer subtype, the study found. They are also much less likely to get the least aggressive type. A report of the research appears in the June 7 issue of the Journal of the American Medical Association.

"The present study adds an important piece to a large puzzle," said senior study author Dr. Robert Millikan. "Previous studies showed that many breast tumors in younger African American women are very fast-growing and hard to treat.

"We found something new: Younger African American breast cancer patients show a high frequency of one of the aggressive subtypes of breast cancer called basal-like," said Millikan, associate professor of epidemiology at the UNC School of Public Health, a UNC Lineberger member and principal investigator of the Carolina Breast Cancer Study (CBCS). The CBCS, one of the largest black breast cancer databases in the United States, is a population-based case-control study that enrolled women with breast cancer from 24 counties of North Carolina as cases, and an equal number of women without breast cancer as controls. Women who consented to the study were interviewed about their histories, and their tumor tissue was collected. The study required extensive cooperation from all of the women who participated in the study, their physicians and pathologists, and a large number of hospitals in North Carolina.

According to JAMA study lead author Dr. Lisa A. Carey, associate professor of medicine in the hematology-oncology division at UNC's School of Medicine, modern technologies such as microarray analysis can reveal the molecular characteristics of cancers and have shown that breast cancer is not one disease. "It is a family of diseases that are biologically different from each other, some more aggressive than others," Carey said. "In this study, using the Carolina Breast Cancer Study, we were looking at how frequently these different subtypes occur in a given population."

DNA microarray analysis allows scientists to determine the expression levels of thousands of genes simultaneously. This can reveal gene expression patterns, which, in turn, enable genomic profiling of tumor cells.

UNC School of Medicine study co-author Dr. Charles M. Perou, assistant professor of genetics, pathology & laboratory medicine, and a Lineberger member, is a pioneer in microarray technology. "Gene expression analysis using DNA microarrays has identified several breast cancer subtypes, including luminal A, luminal B, basal-like and HER2-plus/estrogen receptor-negative," said Perou. "These studies were based on limited sample sets. We wanted to see if we could identify the presence of these subtypes through a population-based study and to find out if they correlate with factors such as age, menopausal status and race."