Other Disease Characteristics
Also using the Black/White Study data,31 Hunter et al. found that a constellation of factors including nuclear grade and having a clinical breast examination, as well as a history of patient delay, explained about half of the excess risk for Stage III and IV cancer in black women with breast cancer. When these factors were compensated for, it reduced the odds ratio (comparative risk) from 2.19 to 1.68. In other words, most of the excess risk was still unaccounted for.
A 2000 SEER-based study of 135,424 breast cancer patients32 comparing survival data in black and white women, found that within each stage category, black women had significantly poorer survival, were less likely to have estrogen- or progesterone-receptor positive tumors (as well as other less aggressive tumor types), and were more likely to have inflammatory breast cancer.
Histologic grade in breast cancer is a prognostic factor. A study done in Metropolitan Detroit33 found that black women were more likely to have tumors of a higher histological grade as well as being hormone receptornegative. In this study of ten thousand women, even after controlling for age, tumor size, stage, grade, socioeconomic status, and quality of care, the relative risk (odds ratio) of mortality for black women was 1.68 that of white women, for women under the age of 50.
Looking at SEER data between 1992 and 1999,34 a 2003 study examined histologic grade, stage and survival for black and white women. The study found that black women had a significantly higher proportion of Stage III tumors than white women. When the study authors corrected the data, they found that “African American women have a less favorable six-year cause-specific survival than Caucasian women for nearly every combination of stage and grade, regardless of age.” While an argument can be made that lack of screening and/or socio-economic factors lead to later stage diagnosis, the study authors point out, “It is not so obvious that low SES or lack of screening account for the higher-grade tumors seen in African American women compared with Caucasian women.” Further, the presence of higher grade tumors at all stages in black women may mean that early detection may not eliminate survival disparities.
Further research is clearly needed to examine the question of differences between racial and ethnic groups with regard to the histology and natural history of the breast cancers they develop. Perhaps a strategy that emphasizes mammography screening may work less well for women who are prone to more aggressive cancers at an early age. We cannot hope to address the disparities in outcomes for minority women until we understand more fully why it is that black women are more likely to die of breast cancer—or, for that matter, what it is about Japanese women's breast cancers that makes them more likely to be detected early and have better outcomes. We should not be dissuaded in this quest by decreasing overall mortality rates, or the apparent increase in early stage diagnosis attributable to mammography screening. The serious, continuing problem of high-risk and metastatic breast cancer should not be obscured by the increasing detection of early disease through screening.
Since the breast cancers of younger women often are aggressive and hormone-receptor negative, disproportions in age distribution across racial and socio-economic groups is also important. An analysis of data from the SEER database of women diagnosed with breast cancer between 1988–199535 found that black women diagnosed with breast cancer were younger, overall, than white women. Approximately 33 percent of black women were less than or equal to 50 years of age when diagnosed with breast cancer. By comparison, slightly less than 25 percent of the white women newly dianosed with breast cancer belonged to that younger age group. There are many such studies; however, care must be taken in understanding attempts to identify what has been referred to as a “black breast cancer.” Observed biological differences, whether innate or acquired from exposures and experiences in a person's lifetime, which may play some contributing role in differing outcomes, can potentially be misused to dismiss important shortcomings in access to care, provider biases, and public education surrounding health behaviors and attitudes.
It's also important to understand that race and ethnicity are far from the clearly definable constructs we often assume that they are, especially when it comes to genetic differences. “There is more variability in genetic traits within racial groups than across racial groups,” points out Catarina Kiefe, of the University of Alabama.36
“Differences in cancer biology between racial groups are unlikely to be responsible for a substantial portion of the survival discrepancy,” members of the Health Outcomes Research Group at Memorial Sloan-Kettering Cancer Center conclude in their 2002 review of the literature on racial discrepancies in cancer survival.37
“Race is not a category that is based on biology,” agrees Harold Freeman, Director of the NIH Center to Reduce Cancer Health Disparities, who sees race as a social construct that changes over time. “This has been agreed upon by most of the predominant members of the scientific community.”38
Nevertheless, observable differences do exist across racial and ethnic lines, some of which may be the result of differing biology and genetics. An example is of higher breast cancer incidence related to BRCA mutations in Ashkenazi Jewish women—the result not of their being Jewish, but of intermarriage within a single population group. Lower incidence of breast cancers in some Asian populations might be another example, although it is far from a simple matter to distinguish between intrinsic and extrinsic factors.