Racial and ethnic disparities in breast tumor aggressiveness might be explained by social factors that influence the developing tumor and place those in disadvantaged groups at higher risk for aggressive breast cancer, according to data presented at the Fifth AACR Conference on The Science of Cancer Health Disparities, held here Oct. 27-30, 2012.
“There is a disparity in the biological aggressiveness of breast cancer,” said Garth H. Rauscher, Ph.D., associate professor of epidemiology at the University of Illinois at Chicago. “We tend to think about biological differences being due to differences in genes, but tumor biology can be affected by social or behavioral factors that are associated with socioeconomic status. Our study highlights the importance of the social environment in influencing tumor biology and ultimately influencing disparities.”
Rauscher and colleagues examined data from a population-based sample of 989 patients with a recent diagnosis of breast cancer (397 non-Hispanic whites, 411 non-Hispanic blacks and 181 Hispanics) from the Breast Cancer Care in Chicago Study. Patients were aged 30 to 79 years and had primary in situ or invasive breast cancer. A total of 742 patients consented to medical record abstraction and had medical record data available for estrogen receptor (ER) and progesterone receptor (PR) status.
Researchers established socioeconomic disadvantage using four measurements: individual income, individual education and two census tract measures of socioeconomic status – concentrated disadvantage and concentrated affluence.
Compared with 12 percent of non-Hispanic white patients, 29 percent of non-Hispanic black patients and 20 percent of Hispanic patients had ER- and PR-negative tumors. Non-Hispanic black and Hispanic patients were also more likely to have lower income and less education and to reside in more disadvantaged and less affluent neighborhoods. In addition, all four measures of socioeconomic disadvantage used in the study were strongly associated with ER/PR-negative status.
“It was interesting to see that the main finding remained unchanged regardless of the measure of socioeconomic status we used,” Rauscher said. “Patient levels of income and education, as well as neighborhood-level measures of socioeconomic status, were each associated with tumor biology. In each instance, lower socioeconomic status was associated with more aggressive breast cancers that lacked these hormone receptors.”
Socioeconomic disadvantage predicts more aggressive estrogen/progesterone receptor negative breast cancer and mediates racial and ethnic disparities in breast cancer aggressiveness
Purpose: Racial and ethnic disparities in breast cancer stage at diagnosis are often attributed to social and behavioral factors (e.g., socioeconomic disadvantage, cultural beliefs, health care access and utilization). However, few studies have directly examined their potential role in generating a disparity in the biological aggressiveness of tumors. It is well established that Hispanic and non-Hispanic (nH) Black breast cancer patients are more likely than their non-Hispanic White counterparts to be diagnosed with more aggressive tumors that are negative for estrogen and progesterone receptors (ER/PR negative). Tumor aggressiveness disparities are important because they contribute not only to disparities in stage at diagnosis, but also to disparities in prognosis more generally. We sought to investigate whether the disparity in ER/PR negative disease might be transmitted through the socioeconomic environment.
Methods: Data were obtained from a population-based sample of 989 recently diagnosed breast cancer patients (397 nH White, 411 nH Black, 181 Hispanic) recruited as part of the Breast Cancer Care in Chicago study, aged 30-79 who had been diagnosed with a primary in situ or invasive breast cancer. Of these, 742 patients consented to medical record abstraction and had available medical record data on ER/PR status. Patients were defined as ER/PR negative if their tumor lacked both ER and PR receptors. Four measures of socioeconomic disadvantage were defined: individual income and education were reported at interview, and census tract measures of socioeconomic status (concentrated disadvantage and concentrated affluence) were derived. In order to assess potential mediation, in age-adjusted logistic regression models we used the method of Karlson, Holm and Breen (2010) to compare rescaled coefficients for the disparity in ER/PR negative status before and after adding all four socioeconomic disadvantage variables to the model.
Results: Compared to nH-Whites, nH-Black and Hispanic patients were more likely to have hormone receptor negative tumors (29% and 20% vs. 12%, respectively, p≤0.001); more likely to have less income and education, and more likely to live in more disadvantaged and less affluent neighborhoods (p<0.001 for all). All four measures of socioeconomic disadvantage were strongly associated with ER/PR negative status (p=0.002 or less). Comparison of rescaled coefficients suggested that at least half of the racial/ethnic disparity in ER/PR negative status could be explained by differences in socioeconomic disadvantage (proportion mediated=51%, p-value for difference in reduced and full models =0.015).
Conclusions: A substantial portion of the racial/ethnic disparity in breast tumor aggressiveness may be transmitted through social influences that impact the biology of the developing tumor, predisposing disadvantaged groups to more aggressive breast cancer. Socioeconomic disadvantage could lead to higher levels of chronic stress, as well as to differences in dietary or hormonal and reproductive histories, any of which might contribute to disparities in tumor biology.
The study was funded by the National Institutes of Health Centers for Population Health and Health Disparities.
American Association for Cancer Research