Breast cancer statistics, 2017, racial disparity in mortality by state

Incidence and mortality rates

Female breast cancer incidence and mortality rates vary substantially by race/ethnicity in the United States (Fig. 1). Non-Hispanic white (NHW) and non-Hispanic black (NHB) women have higher breast cancer incidence and death rates than women of other race/ethnicities; API women have the lowest incidence and death rates. Although the overall breast cancer incidence rate during 2010 through 2014 was slightly (2%) lower in NHB women (125.5 per 100,000) than in NHW women (128.7 per 100,000), the breast cancer death rate during 2011 through 2015 was 42% higher in NHB women (29.5 per 100,000) than in NHW women (20.8 per 100,000). Racial differences in breast cancer incidence rates vary by age (Fig. 2). Compared with NHW women, NHB women have higher breast cancer incidence rates before age 40 years but lower rates at ages 65 to 84 years. NHB women are more likely to die from breast cancer at every age.

Figure 3 shows racial/ethnic variation in incidence rates by breast cancer subtype. Gene expression profiling techniques have allowed researchers to identify at least 5 different molecular subtypes (luminal A, luminal B, human epidermal growth factor receptor 2 [HER2] overexpression, basal, and normal-like tumors), which are biologically variable in presentation, response to treatment, and outcomes and may be associated with distinct etiology.[14, 15] These molecular subtypes are approximated using routinely evaluated immunohistochemical markers, including the presence or absence of HRs (ER or PR); (HR-positive/HR-negative) and expression of the HER2 (HER2-positive/HER2 negative) protein.[16] The HR-positive/HER2 negative (luminal A) breast cancers are the most common subtype in each racial/ethnic group; however, rates range from 53 cases per 100,000 in Hispanics to 82 cases per 100,000 in NHW. Lower overall breast cancer incidence rates in AI/AN, Hispanic, and API women are primarily driven by lower rates of the HR-positive/HER2-negative subtype. In contrast, incidence rates for triple-negative breast cancers (HR-negative/HER2-negative), most of which are the basal subtype, are twice as high in NHB women (24 per 100,000) compared with NHW women (12 per 100,000), which is the racial/ethnic group with the second highest rate. Importantly, studies suggest that the distribution of breast cancer subtypes may also vary within the broad racial/ethnic groups described here. For example, although overall rates of HR-negative/HER2-positive breast cancers in API women are similar to the rates in other groups, an analysis of California women by Asian ethnic subgroup reported that Korean, Filipina, Chinese, and Southeast Asian women had a higher risk of HR-negative/HER2-positive breast cancers compared with NHW women, whereas Japanese and American Indian women had lower risk for this subtype.[17] Racial and ethnic differences in breast cancer subtypes may reflect variation in the prevalence of breast cancer risk factors, particularly reproductive factors, which are most strongly associated with HR-positive breast cancers[15, 18] but also appear to reflect ancestry-related genetic variations.[19-21]

Stage distribution and survival

Racial and ethnic variations in breast cancer stage at diagnosis and 5-year cause specific survival are shown in Figure 4. NHW and API women have the highest proportions of localized breast cancers (range, 65%-67%) and the lowest proportions of regional (range, 27%-30%) stage disease. In contrast, NHB and Hispanic women have lower proportions of localized breast cancers (range, 57%-59%) and higher proportions of regional (35%) stage disease. Distant-stage disease represented 9% of diagnoses among NHB women, compared with 5% to 6% of diagnoses in other racial/ethnic groups.

Cause-specific survival (ie, the probability of not dying of breast cancer within a specified number of years after diagnosis) is used instead of relative survival to describe survival in racial and ethnic minorities, because reliable estimates of life expectancy are not available for some racial/ethnic groups. For each known stage of disease, 5-year breast cancer survival is highest for API women and lowest for NHB women (Fig. 4). Racial/ethnic differences in survival in part reflect the variation in the distribution of breast cancer subtypes (Fig. 3).

Incidence

Much of the historic increase in breast cancer incidence rates reflect changes in reproductive patterns, such as delayed childbearing and having fewer children, which are recognized risk factors for breast cancer.[22, 23] Incidence rates of in situ and invasive breast cancer rose rapidly during the 1980s and 1990s (Fig. 5), largely because of increased use of mammography screening in the United States. The widespread uptake of mammography screening inflated the incidence rate, because cancers were being diagnosed 1 to 3 years earlier than they would have been in the absence of screening, and screening also may have led to the detection of indolent cases. Invasive breast cancer rates stabilized between 1987 and 1994, followed by a slower increase during the late 1990s. The continued increase particularly among older women may reflect rising rates of obesity and the use of menopausal hormones, both of which increase the risk of postmenopausal breast cancer, as well as further increases in the prevalence of mammography screening.[24] Around the year 2000, incidence rates began to decline among women ages 50 years and older; and, between 2002 and 2003, breast cancer rates decreased nearly 7%, likely because of the decreased use of menopausal hormones after publication of the Women's Health Initiative randomized trial results linking the use of estrogen plus progesterone menopausal hormone therapy to breast cancer and heart disease.[25-27] The decline occurred primarily in white women and in those who had HR-positive disease.[26, 28] The drop in incidence may also reflect in part the small declines in mammography screening since 2000. The percentage of women aged 40 years and older who reported having a mammogram within the past 2 years increased from 29% in 1987 to 70% in 2000 and dropped to 64% in 2015.[29]

Trends in breast cancer incidence rates by race/ethnicity are shown in Figure 6. During 2005 through 2014 (the most recent 10 years of data available), overall breast cancer incidence rates increased among API (1.7% per year), NHB (0.4% per year), and Hispanic (0.3% per year) women but were stable among NHW and AI/AN women. Incidence rates for AI/AN women are less stable than for other racial and ethnic groups, because high-quality data for this group are only available from limited geographic areas. We further examined breast cancer incidence trends by HR status for the 5 major US racial/ethnic groups during 2004 through 2014 (Fig. 7). In all racial/ethnic groups, incidence rates increased for HR-positive (ER-positive or PR-positive) breast cancers and decreased for HR-negative tumors.

Mortality

Overall breast cancer death rates increased by 0.4% per year from 1975 to 1989 but since have decreased rapidly, for a total decline of 39% through 2015. As a result of this decline, 322,600 breast cancer deaths have been averted in US women through 2015. The decrease occurred in both younger and older women but has slowed among women younger than 50 years since 2007. Declines in breast cancer mortality rates have been attributed to both improvements in treatment (eg, adjuvant chemotherapy and hormonal therapy in the 1980s and targeted therapies in the 1990s) and early detection by mammography.[30, 31]

Not all women have benefited equally from these improvements, as evidenced by variation in mortality trends by race/ethnicity (Fig. 8). A striking divergence in long-term breast cancer mortality trends between black and white women emerged in the early 1980s and continued to widen over the last several decades, but recent data suggest that the racial disparity may be stabilizing. The mortality gap that developed more than 30 years ago may reflect the unmasking of differences in tumor phenotype distribution between blacks and whites. Outcome improvements resulting from endocrine therapy with tamoxifen (which was approved by the US Food and Drug Administration in 1977) were being realized during that timeframe but to a lesser degree among black women because of their lower rates of HR-positive disease. In 2011, the disparity peaked with death rates 44% higher in NHBs than in NHWs (mortality rate ratio [MRR], 1.44; 95% confidence interval [CI], 1.40-1.48). The racial disparity has been relatively constant over the past several years; in 2015, breast cancer death rates were 39% higher in black women than in white women (MRR, 1.39; 95% CI, 1.35-1.43). In addition, the most recent data indicate that breast cancer mortality rates have decreased in all major racial/ethnic groups in the United States. From 2006 through 2015, breast cancer death rates declined annually by 2.6% in AI/ANs, 1.8% in NHWs, 1.5% in NHBs, 1.4% in Hispanics, and 0.9% in APIs. Notably, the decline among AI/AN women began in 2005, more than a decade later than other racial and ethnic groups.

Survival

More than 3.5 million US women with a history of breast cancer were alive on January 1, 2016.[32] Figure 9 present trends in 5-year relative survival for breast cancer by race and stage at diagnosis from 1975 through 1977 to 2007 through 2013. There were significant survival gains for each stage of disease among both black women and white women. The largest improvement in survival was for those with regional-stage disease, which increased from 68% to 89% for white women and from 55% to 81% for black women. Survival gains for distant-stage disease were larger for white women (19% to 37%) than for black women (16% to 26%). Improvements in breast cancer stage-specific survival reflect treatment advances as well as decreases in tumor size within each stage of disease.[33, 34]

Geographic variations in incidence, mortality, and mammography

State variations in mammography screening prevalence, breast cancer incidence and mortality rates and rate ratios, and the proportion of in situ breast cancer diagnoses are presented in Table 3. In 2014, the reported rates of mammography within the past 2 years among white women ages 40 years and older ranged from 62% in Alaska to 83% in Massachusetts. Thirty-six states had sample sizes large enough to estimate the prevalence of recent mammography screening among black women ages 40 years and older, which ranged from 54% in Nevada to 89% in California.

Historically, breast cancer incidence rates were higher in white women than in black women; however, incidence rates converged for women living in the SEER 9 registry areas in 2012. Furthermore, among 43 states and the District of Columbia with data on incidence rates for both blacks and whites, rates were significantly higher for black women living in 8 mostly Southern states (Alabama, Indiana, Louisiana, Michigan, Mississippi, Missouri, North Carolina, and Virginia) and were not significantly different in 20 other states (Table 3). In 15 states and the District of Columbia, incidence rates remained lower in NHB women compared with white women. When comparing incidence rates among states, it is important to consider that incidence rates reflect the intensity of screening as well as disease occurrence. The percentage of in situ breast cancers, an indicator of mammography utilization, varied from 15% in Wyoming and Oklahoma to 24% in the District of Columbia and New York among whites and from 11% in West Virginia to 26% in Connecticut and Massachusetts among blacks.

In every US state, breast cancer death rates are higher in NHB women than in NHW women. Breast cancer death rates ranged from 17.5 to 24.5 per 100,000 in North Dakota and Nevada, respectively, among white women and from 20.6 to 34.4 per 100,000 in Massachusetts and the District of Columbia, respectively, among NHB women. The excess death rate in blacks, as measured by the MRR, also varies widely in the United States, ranging from 20% in Nevada (MRR, 1.20; 95% CI, 1.01-1.42) to 66% in Louisiana (MRR, 1.66; 95% CI, 1.54, 1.79) (Fig. 10). Notably, in 7 states, breast cancer death rates were not statistically different between NHB and NHW women, although this may reflect a lack of statistical power (small numbers of breast cancer deaths among black women), except for Massachusetts (MRR, 1.08; 95% CI, 0.94-1.24), Connecticut (MRR, 1.10; 95% CI, 0.94-1.28), and perhaps Delaware (MRR, 1.22; 95% CI, 1.00-1.49). Furthermore, Connecticut and Massachusetts are the states with the lowest breast cancer death rates and the highest proportions of in situ diagnoses among NHB women.