Higher rates of hypertension in African American women compared with white women may account for some of the previously found racial disparities in overall survival among women with breast cancer, according to new research.
UCSF epidemiologist Dejana Braithwaite, PhD, is among the significant number of cancer researchers now exploring why it is that African American women diagnosed with breast cancer fare worse, on average, than white women diagnosed with the disease.
Results of a new study led by Braithwaite and senior investigator Laura Esserman, MD, co-leader of the Breast Oncology Program at the UCSF Helen Diller Family Comprehensive Cancer Center, indicate that hypertension alone accounts for about 30 percent of the disparity in survival between African American and white women diagnosed with breast cancer. The results were published online in the International Journal of Cancer in October and will appear in the March 1, 2009, print edition.
Other co-authors of the study were Martin Tammemagi, PhD; Dan Moore, PhD; Elissa Ozanne, PhD; Robert Hiatt, MD, PhD; Jeff Belkora, PhD; Dee West, PhD; William Satariano, PhD; and Michael Liebman, PhD.
“Hypertension is a very common condition among African Americans,” Braithwaite says. People who are obese or who have diabetes often are hypertensive. But in this study, hypertension remained important even after the impact of obesity, diabetes and other medical conditions was accounted for, Braithwaite says. While many of these so-called comorbidities had been taken into account in previous studies by researchers using the well-known Charlson comorbidity index, hypertension had not been included in that tool.
Nonetheless, Braithwaite says, “In our study, hypertension prior to cancer diagnosis was an independent predictor of decreased survival.”
It has been known for years that African American women are more likely to be diagnosed with breast cancer at younger ages, and more often with tumors having biological markers associated with a worse prognosis. In addition, poor access to treatment and screening often is blamed for the disparity in survival between races.
But even studies that correct for differences in tumor severity and treatment find survival differences, which is what Braithwaite and Esserman have been seeking to explain.
The new study included 416 African American women and 838 white women, all of whom had health insurance through Kaiser Permanente Northern California. Braithwaite and colleagues examined information obtained from the medical records of women diagnosed with breast cancer between 1973 and 1986. They looked at the records for these women from the time of diagnosis through 1999, and obtained additional information from the Northern California Cancer Center registry.
After an average follow-up time of nine years, 40 percent of the African American women had died from any cause, compared with 33 percent of white women. The researchers found that hypertension affected survival even after controlling for other comorbid conditions, including age, race, tumor characteristics and cancer treatment.
“It is important to manage hypertension, as it may be beneficial for overall survival, particularly in African American patients,” Braithwaite says.
According to Esserman, “It is critical to understand the biological explanation for the higher mortality seen in African American women if we are going to do a better job of tailoring treatments and making them more effective.
“Specifically, this study helps us understand the host environment that might be more conducive to the development of cancer – for example, that the forces putting African American women at risk for hypertension may also be contributing to increased risk for breast cancer.”
The researchers have not ruled out the possibility that hypertension might actually affect the course of already diagnosed breast cancer in some cases, although it is not clear how that could be. Preliminary results suggest that it may be worth investigating whether there indeed is an association between hypertension and not only the overall risk of death, but also the specific risk of dying of breast cancer.
Braithwaite is now investigating that question in a new study. “I would not jump to make that conclusion at this stage,” she cautions. “It is imperative that we confirm these findings, as they will likely uncover novel opportunities to intervene for improved survival among African American women with breast cancer. With mortality rates nationwide over 35 percent higher in this population compared to white women, we need to find solutions to this problem.”
Dejana Braithwaite, C. Martin Tammemagi, Dan H. Moore, Elissa M. Ozanne, Robert A. Hiatt, Jeff Belkora, Dee W. West, William A. Satariano, Michael Liebman and Laura Esserman
International Journal of Cancer (published online Oct. 9, 2008) 124(5):1213-1219
Abstract | Full Text | PDF
UCSF Breast Oncology Program
Helen Diller Family Comprehensive Cancer Center