Color of Breast Cancer: Why Blacks and Whites are Different
One of the many mysteries surrounding breast cancer is why black women and white women have different experiences with the disease. A possible explanation for why blacks and whites are different has been discovered by experts at the North Shore-LIJ Health System and the Feinstein Institute for Medical Research and being presented at the 2012 American Society of Clinical Oncology annual meeting.
The color of breast cancer
In the United States, there are significant differences in the rates of new cases of and deaths from breast cancer among women. The highest number of new cases of breast cancer occur among white women, at 123.5 per 100,000, compared with 113.0 per 100,000 among black women.
But when you look at death rates from breast cancer, black women fare far worse than white women: per 100,000 women there are 33.0 deaths among blacks and 23.9 among whites. In addition, the five-year survival rates are 90% for white women and 78% for black women, which is the lowest of any other ethnic and racial group in the United States, according to the American Cancer Society.
Among women younger than 40, blacks have a higher incidence of breast cancer than whites, and they are more likely to be diagnosed with larger tumors than white women. Black women also experience a more aggressive form of breast cancer that appears nearly 10 years before those seen in white women.
The discovery made by the researchers and physicians in this new study focused on a genetic marker called microRNA, which is found in the DNA (deoxyribonucleic acid). It's known that the expression of microRNA is not the same between black and white women, and the investigators wanted to find out why this is so and if the variation might explain the difference in survival between white and black women who have breast cancer.
The investigators collected blood samples from 32 women, 16 white and 16 black. Ten women had stage III triple-negative breast cancer (5 black, 5 white), 10 had stage III estrogen-receptor or progesterone-receptor positive breast cancer (5 black, 5 white), and 12 women served as controls (6 black, 6 white). All the samples were analyzed for microRNA profiles.
Analysis of the blood samples revealed the following:
- White patients with triple-negative breast cancer overexpressed 20 microRNAs, which was 15 times greater than seen in controls
- None of the microRNAs seen in the women with triple-negative breast cancer were seen in the black patients
- Black women with breast cancer overexpressed only six microRNAs (15 times greater than seen in controls), and none of these microRNAs were found in the white patients who had triple-negative breast cancer
- Four microRNAs seen in black patients and 8 microRNAs seen in white patients were not previously reported in association with breast cancer. This finding indicates that these microRNAs may have a role in how women react to cancer.
What the study findings suggest
What do the differences in the microRNA expressions between black breast cancer patients and white breast cancer patients mean? For one thing, they "may provide insight into answering why, when receiving similar treatments, outcomes are different between African Americans and Caucasians," noted Iuliana Shapira, MD, director of the Cancer Genetics Program at the North Shore-LIJ Health System's Monter Cancer Center.
The study's findings also indicate that women with breast cancer who have the worst outcomes may have microRNAs that promote cancer, and that white women may have microRNAs that protect them against cancer while black women do not express those microRNAs.
"Methods to increase microRNAs in the blood before surgery for cancer, such as giving chemotherapy before surgery for cancer, may improve survival rates in African American women with triple-negative breast cancer," offered Shapira. Overall, the study casts new light on the color of breast cancer and offers researchers new information regarding differences between how white women and black women experience the disease.
American Cancer Society Surveillance Health Policy Research 2010
American Cancer Society, Cancer Facts & Figures for African Americans, 2011-2012
American Society of Clinical Oncology annual meeting 2012