Science Spotlight

Socioeconomic factors behind breast cancer disparities

From the Li Lab, Public Health Sciences Division.

Invasive breast cancer is the most commonly diagnosed cancer among Hispanic women in the United States, as well as the leading cause of cancer death. As Hispanics comprise 17% of the US population, understanding why they collectively experience worse breast cancer outcomes is an important public health challenge. While previous studies have singularly evaluated potential clinical, molecular, and socioeconomic reasons for these disparities, a comprehensive evaluation of these factors together has been lacking. In a recent issue of Breast Cancer Research and Treatment, Dr. Christopher Li in the Public Health Sciences Division reports that the majority of these disparities appear to be the result of differences in health insurance and socioeconomic status.

To evaluate these different factors together, the authors utilized data from the California Cancer Registry from 2004-2014. This provided information on breast cancer incidence, cancer stage, tumor subtype, clinical treatment, and insurance status. Breast cancer survival was assessed by linkage to vital registration databases, while census data was used to estimate neighborhood socioeconomic status. Together, the authors were able to characterize difference between nearly 30,000 Hispanic and 100,000 non-Hispanic white women.

The authors first investigated whether there were differences in which molecular subtypes of breast cancer were experienced by these groups. Said senior author Dr. Li, “we found that Hispanic women are more frequently diagnosed with more aggressive molecular subtypes of breast cancer, including both triple-negative and HER2+ disease.” These patterns of higher odds of aggressive tumor subtypes were observed regardless of age at diagnosis, stage at diagnosis, or neighborhood socioeconomic status. Said Li, “both of these subtypes have a poorer prognosis than the more common hormone receptor positive forms of breast cancer.”

Mortality rate ratios adjusting for different factors
Plot of mortality rate ratio and 95% confidence interval for breast cancer mortality comparing Hispanic and non-Hispanic white women. Plot shows the result for the baseline model and after adjustment for clinical or sociodemographic factors (nSES = neighborhood socioeconomic status), with a * denoting a statistical significant difference. Image provided by Jonathan Kocarnik

Next the authors also evaluated breast cancer survival, and found that Hispanic women had a 24% higher mortality rate than non-Hispanic white women. To identify what might account for this disparity, additional analyses for various factors were performed. Adjusting for the tumor subtype did not substantially reduce the difference in cancer mortality, while adjusting for tumor characteristics such as cancer stage, tumor grade, and histology did lower the difference to 5% (see figure). The biggest difference was observed when adjusting for sociodemographic factors: when health insurance and neighborhood socioeconomic status were included in the model, the survival difference between these groups disappeared. Said Li, “while we observed that Hispanic breast cancer patients continue to experience higher rates of mortality, we found that much of this disparity is likely attributable to differences related to access to care.”

The results of this large population-based study show that, for California at least, the combined effect of health insurance and neighborhood socioeconomic status likely serve as the fundamental causes of why Hispanic patients are more likely to die of breast cancer compared to non-Hispanic white women. These results further suggest that the observed disparities in breast cancer survival are not due to physiologic differences but broader social disparities. Said Li, “on-going efforts that address socioeconomic disparities are needed to eliminate these long persisting disparities.” Though the Affordable Care Act has helped to reduce the uninsured rate in California, from 16% in 2013 to 9% in 2016, Hispanics continue to lag behind. Additional efforts to enable health care access, reform the health care system, and raise socioeconomic standards are likely to create substantial strides in reducing these differences in breast cancer mortality.



Martínez ME, Gomez SL, Tao L, Cress R, Rodriguez D, Unkart J, Schwab R, Nodora JN, Cook L, Komenaka I, Li C. Contribution of clinical and socioeconomic factors to differences in breast cancer subtype and mortality between Hispanic and non-Hispanic white women. Breast Cancer Res Treat 2017. doi: 10.1007/s10549-017-4389-z.



Funding for this study was provided by the National Cancer Institute, the National Institutes of Health, the Centers for Disease Control and Prevention’s National Program of Cancer Registries, the California Department of Public Health, the Specialized Cancer Center Support Grant, the SDSU/UCSD Comprehensive Cancer Center Partnership, and the Stanford Cancer Institute.