The Emergence of Racial Disparity in Breast Cancer Mortality in the United States
In the United States, age-adjusted breast cancer mortality is approximately 40% higher in black women than in non-Hispanic white women (27.7 versus 20.0 deaths per 100,000 women from 2014 to 2018 ), despite a lower incidence among black women (125.8 versus 139.2 cases per 100,000 women) (see table). It may therefore surprise many clinicians that before 1980 breast cancer mortality was slightly lower in black women than in white women (see chart). Mortality rates diverged sharply after 1980, and this disparity persists.1.2
What triggered the divergence in breast cancer mortality by race in the 1980s? Age-period-cohort (APC) models provide important clues because they can be used to distinguish 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, while trends based on birth cohort reflect the variation in risk factors among people born at different times.2
In previous work, one of us reported that APC models showed pronounced racial divergence in breast cancer mortality by calendar period, but not by birth cohort.2 The emergence of racial disparity in breast cancer mortality can therefore be attributed to a calendar period effect rather than a birth cohort effect, meaning that the introduction of new medical interventions was likely the triggering factor. In the 1980s, two medical interventions were widely implemented in the United States for the management of breast cancer – mammography screening and adjuvant hormone 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 have no health insurance or inadequate coverage, which has limited their access to mammography screening and adversely affected treatment decision-making. In the 1980s, for example, mammography screening rates were considerably lower among black women than among white women, although the rates are now similar.2
Mammography screening and hormone therapy primarily benefits patients with hormone receptor (HR) positive breast cancer, the most common subtype in black and white women.2.3 Mammography screening preferentially detects and targets hormone therapy 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 screening mammography examinations as symptomatic (i.e., palpable) cancers.3 HR-negative cancers include triple-negative cancers (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 in younger women than other breast cancer subtypes. Compared to non-Hispanic white women, black women have a 65% higher rate of any HR-negative cancer (29.3 versus 17.7 cases per 100,000 women from 2014 to 2018) and an 81% higher rate of cancer triple negative breast (21.9 versus 12.1 cases per 100,000 women); Black women therefore benefited less from the introduction of mammography screening and adjuvant hormone therapy.1
Some researchers have suggested that hereditary factors explain the disproportionately high rates of HR-negative and triple-negative breast cancer among black women, since most black American women trace their ancestry to western sub-Saharan Africa, where the 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 diverse American racial groups should have remained relatively stable in recent years. Yet, from 1992 to 2016, the incidence of HR-negative breast cancer declined among women of all races in the United States, and there was considerable variation in the rate of decline between racial groups and among women of the same breed from different geographical regions.5 Declines were slowest among black women, and reductions were smaller among white women from less affluent regions than among white women from wealthier regions, suggesting that the social determinants of health (i.e., i.e. structural racism and built environments) not only influence access and quality of health care, but also the development of HR-negative breast cancers.5
Since 1990, there has been an overall 40% reduction in breast cancer mortality in the United States. Screening, adjuvant systemic therapies, and decreasing the incidence of HR-negative cancer have contributed to the reduction in mortality among black and white women, although – as with the incidence of HR-negative cancer – the rates of decline have been uneven. If all people with breast cancer benefited equally from effective medical interventions, racial differences in mortality for different tumor subtypes would largely reflect differences in incidence. However, breast cancer data from the National Cancer Institute’s Surveillance, Epidemiology, and Final Outcomes Registry indicate substantial racial disparities in mortality for HR-positive and HR-negative cancers that cannot be explained solely. by differences in incidence.
Mortality in patients with a particular tumor subtype is a reflection of incidence, case detection rates, and treatment. HR-positive breast cancer mortality is 19% higher in black women than in white women, despite a 22% lower incidence in black women, and HR-negative breast cancer mortality is more than two times higher in black women than in white women—a difference much larger than the 65% relative difference in incidence. The mortality gap for the two tumor subtypes indicates that black women may face significant barriers to obtaining timely, high-quality medical care, although differences in biological factors among patients with sub -Specific tumor types, such as variations in grade and HER2 status, as well as differences in treatment response and adherence within patient groups, could also partly explain the disparity.
The difference in breast cancer mortality between black and white women varies widely across the United States, partly reflecting variation in the extent to which states facilitate universal access to high-quality health care. .1 Lack of or inadequate health insurance coverage limits access to prompt and effective treatment2; according to data from the Kaiser Family Foundation, more than 11% of non-elderly blacks are uninsured, compared to about 8% of non-elderly whites. 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 reduce the racial divide in breast cancer mortality.
Prior to 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 watershed moment, and substantial overall reductions in breast cancer mortality followed. A troubling consequence of the implementation of these medical interventions, however, has been the emergence of a large racial disparity in breast cancer mortality in the United States. Black women have benefited less from these procedures than white women, and they have significantly higher rates of HR-negative tumors, which generally have a poorer prognosis than other tumors. From 2014 to 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 that supporting research into the prevention and treatment of triple-negative breast cancer should be a national priority, as such research will be essential in mitigating racial disparities in outcomes and reducing global breast cancer mortality. Given that the overall incidence of breast cancer remains lower among black women than among white women in the United States, ensuring universal access to high-quality medical care can significantly reduce the racial disparity in mortality by breast cancer in the United States.