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The Emergence of the Racial Disparity in U.S. Breast-Cancer Mortality & More Trending News

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Incidence of Breast Cancer and Breast-Cancer Mortality among Black Women and Non-Hispanic White Women in the United States According to HR Status, 2014 through 2018.
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Trends in Breast-Cancer Mortality among Black Women and White Women in the United States, 1970 through 2018.

Age-standardized breast-cancer mortality (deaths per 100,000 women per year) was calculated with the use of SEER*Stat software, version 8.3.9.2, on the basis of the underlying cause of death reported on death certificates. Before 1990, the Census Bureau provided county-level population estimates according to three racial categories: White, Black, and other races. Thus, White race includes Hispanic and non-Hispanic White persons, and Black race includes Hispanic and non-Hispanic Black persons. Adapted and updated from DeSantis et al.1

In the United States, age-adjusted breast-cancer mortality is about 40% higher among Black women than among non-Hispanic White women (27.7 vs. 20.0 deaths per 100,000 women from 2014 through 2018), despite a lower incidence among Black women (125.8 vs. 139.2 cases per 100,000 women) (see table). It may therefore come as a surprise to many clinicians that before 1980, breast-cancer mortality was slightly lower among Black women than among White women (see graph). The death rates diverged sharply after 1980, and this disparity has been persistent.1,2

What triggered the divergence in breast-cancer mortality according to race in the 1980s? Age–period–cohort (APC) models provide important clues, since they can be used to distinguish among changes in mortality that are based on age at death, year of death (calendar period), or year of birth (birth cohort).2 Trends based on calendar period reflect changes in exposures affecting the entire population during a particular era, such as access to new medical interventions, whereas trends based on birth cohort reflect variation in risk factors among people born during different eras.2

In previous work, one of us reported that APC models showed a pronounced racial divergence in breast-cancer mortality according to calendar period, but not according to birth cohort.2 The emergence of the racial disparity in breast-cancer mortality can therefore be attributed to a calendar-period effect rather than a birth-cohort effect, which means that the introduction of new medical interventions was most likely the precipitating factor. In the 1980s, two medical interventions were widely implemented in the United States for breast-cancer management — mammography screening and adjuvant endocrine therapy — and racial disparities in access to these interventions, as well as in their effects, probably precipitated the divergence in mortality.2 Black women are more likely than White women to lack health insurance or to have inadequate coverage, which has limited their access to mammography screening and adversely affected therapeutic decision making. In the 1980s, for example, mammography-screening rates were substantially lower among Black women than among White women, although the rates are now similar.2

Both mammography screening and endocrine therapy benefit primarily patients with hormone receptor (HR)–positive breast cancers, the most common subtype among both Black and White women.2,3 Mammography screening preferentially detects, and endocrine therapy targets, HR-positive tumors, which are more indolent than HR-negative tumors and therefore spend more time in the preclinical phase.2,3 In contrast, HR-negative tumors are often detected during the interval between mammography-screening exams as symptomatic (i.e., palpable) cancers.3 HR-negative cancers include triple-negative (i.e., estrogen receptor–negative, progesterone receptor–negative, and human epidermal growth factor receptor type 2 [HER2]–negative) breast cancers, an aggressive subtype that is frequently diagnosed at later stages and among younger women than other breast cancer subtypes. As compared with non-Hispanic White women, Black women have a 65% higher rate of any HR-negative cancer (29.3 vs. 17.7 cases per 100,000 women from 2014 through 2018) and an 81% higher rate of triple-negative breast cancer (21.9 vs. 12.1 cases per 100,000 women); Black women have thus derived less benefit from the introduction of mammography screening and adjuvant endocrine therapy.1

Some investigators have suggested that hereditary factors account for the disproportionately high rates of HR-negative and triple-negative breast cancer among Black women, since most U.S. Black women trace their ancestry to western sub-Saharan Africa, where HR-negative breast cancers are common.4 If hereditary factors were the sole determinant of hormone-receptor biology, however, the incidence of HR-negative breast cancer among various U.S. racial groups should have remained relatively stable in recent years. Yet from 1992 to 2016, the incidence of HR-negative breast cancer decreased among women of all races in the United States, and there was considerable variation in the rate of decline among racial groups and among women of the same race from different geographic regions.5 Declines were slowest among Black women, and reductions were smaller among White women from less affluent regions than among White women from more affluent regions, which suggests that social determinants of health (i.e., structural racism and built environments) influence not only access to and quality of health care but also the development of HR-negative breast cancers.5

Since 1990, there has been a 40% overall reduction in breast-cancer mortality in the United States. Screening, adjuvant systemic therapies, and decreases in the incidence of HR-negative cancer have contributed to reductions in mortality among both Black and White women, although — as in the case of the incidence of HR-negative cancer — rates of decline have been uneven. If all people with breast cancer benefited equally from effective medical interventions, racial differences in mortality for individual tumor subtypes would largely reflect differences in incidence. However, breast-cancer data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results registry indicate substantial racial disparities in mortality for both HR-positive and HR-negative cancers that cannot be explained by differences in incidence alone.

Mortality among patients with a particular tumor subtype is a reflection of incidence, case-ascertainment rates, and treatment. Mortality for HR-positive breast cancer is 19% higher among Black women than among White women, despite a 22% lower incidence among Black women, and mortality for HR-negative breast cancer is more than twice as high among Black women as among White women — a disparity that is substantially larger than the 65% relative difference in incidence. The mortality gap for both tumor subtypes indicates that Black women may face substantial barriers to obtaining timely, high-quality medical care, although differences in biologic factors among patients with particular tumor subtypes, such as variations in grade and HER2 status, as well as differences in response and adherence to treatments within patient groups, could also partially account for the disparity.

The difference in breast-cancer mortality between Black women and White women varies substantially within the United States, which partly reflects variation in the extent to which states facilitate universal access to high-quality health care.1 Lack of health insurance coverage or inadequate coverage limits access to timely, effective treatments2; according to data from the Kaiser Family Foundation, more than 11% of nonelderly Black people are uninsured, as compared with about 8% of nonelderly White people. Universal health care coverage could reduce disparities in treatment for cancers of all subtypes, including triple-negative breast cancer. Removing barriers to health care access could therefore mitigate the racial divide in breast-cancer mortality.

Before the 1980s, overall breast-cancer mortality in the United States was remarkably stable for several decades, and the mainstay of treatment was mastectomy. The widespread use of screening mammography and adjuvant systemic therapy beginning in the 1980s was a critical turning point, and substantial overall reductions in breast-cancer mortality followed. A troubling consequence of the implementation of these medical interventions, however, was the emergence of a large racial disparity in breast-cancer mortality in the United States. Black women have derived less benefit from these interventions than White women, and they have substantially higher rates of HR-negative tumors, which generally carry a poorer prognosis than other tumors. From 2014 through 2018, a total of 56% of the difference in breast-cancer deaths between Black and White women could be attributed to HR-negative cancer. We believe supporting research on the prevention and treatment of triple-negative breast cancer should be a national priority, since such research will be essential for mitigating racial disparities in outcomes and reducing global breast-cancer mortality. Because overall breast-cancer incidence remains lower among Black women than among White women in the United States, ensuring universal access to high-quality medical care can substantially narrow the racial disparity in U.S. breast-cancer mortality.

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