Why Do Black Women Have Higher Breast Cancer Morality Rates?

a report from researchers at the Centers for Disease Control and Prevention (CDC) finds that despite significant progress in breast cancer detection and treatment, black women experience higher death rates even though they have a lower incidence of breast cancer compared to white women. Researchers analyzed breast cancer incidence, stage at diagnosis, and mortality rates for 2005–2009 for women in the United States and for each state, then calculated black to white mortality ratios and mortality to incidence ratios by race. They found despite having lower incidence rates, black women had a 41% higher breast cancer death rate. More black women were diagnosed at regional or distant cancer stage compared with white women (45% versus 35%). For every 100 breast cancers diagnosed, black women had nine more deaths than white women (27 deaths per 100 breast cancers diagnosed among black women compared with 18 per 100 among white women).

a cancer research consortium headed by investigators at Vanderbilt-Ingram Cancer Center (VICC) and two other institutions, today received $12 million in federal funding to help determine why african-american women die at a higher rate and have more aggressive breast cancer than white women. The grant, which was awarded by the National Cancer Institute (NCI), part of the National Institutes of Health, is based on the premise that having a better understanding of the biology–and, in particular, the genetics–of breast cancer in african-american women will lead to better prevention and treatment.

although breast cancer incidence rates are lower in african-american women than comparable White populations, their morbidity and mortality rates are higher.1–3 african-american women tend to present with late stage disease, which may reflect poor access to or utilization of health services, or indeed more aggressive forms of the disease.4–7 Insight into reasons for these differences may be gained by studying breast cancer patterns in other populations across the african diaspora. Of particular interest are comparisons with african-Caribbean populations, which share a common heredity with african-americans and West africans.8 as Caribbean countries undergo developmental changes consistent with the latter stages of the epidemiological transition,9 high rates of lifestyle-related chronic diseases are now prevalent,10–12 underpinning the similar health profiles in african-Caribbean and african-american populations. There remains, however, a dearth of relevant epidemiological data about breast cancer, reported to be the principal malignancy affecting women in the region.13

The aim of this report is to provide the first population-based data of breast cancer incidence and trends in mortality for women in Barbados, West Indies. Barbados is an independent Caribbean island nation in the western atlantic Ocean, with an estimated population of about 270,000. at the 2000 household census, over 90% of all Barbadians were of african descent, approximately 4% were of European origin, while South asian and other ethnic groups accounted for less than 2% of the population.14 The geographic features of the island, its comprehensive publicly-funded healthcare system, centralized pathology, radiology and other clinical specialist services, as well as cooperation of clinical colleagues, have facilitated the development of a comprehensive epidemiologic study of breast and prostate cancer. The Barbados National Cancer Study commenced in 2002 with the aim of describing the incidence and risk factors (environmental and genetic) for breast and prostate cancer. Our study provided infrastructure and allowed data collection for this report.

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“Health disparities are a problem of great concern for the NCI and one that we are zeroing in on as evidenced by this grant,” said Douglas Lowy, M.D., acting director of the NCI.

“This crucial federal funding support will enable a trans-institutional collaboration between VICC cancer investigators and their colleagues at other major institutions to explore the biological and genetic underpinnings of breast cancer in african-american women who have been suffering disproportionately from this disease,” said Jennifer Pietenpol, Ph.D., executive vice president for Research at Vanderbilt University Medical Center and director of VICC.

Zheng conceived the study and helped recruit other prominent investigators to form the consortium.The research team is being led by Principal Investigator Wei Zheng, M.D., Ph.D., MPH, VICC, Nashville; Christopher Haiman, Sc.D., University of Southern California, Los angeles; and Julie Palmer, Sc.D., MPH, Boston University.

“Breast cancer exacts a particularly heavy toll on african-american women. This study will generate enormous resources and greatly expand our research capacity to illuminate the biological and genetic basis of this common cancer,” said Zheng, the anne Potter Wilson Professor of Medicine, director of the Vanderbilt Epidemiology Center and chief of the Division of Epidemiology. “I am truly privileged to work alongside so many outstanding researchers in discovering innovative answers to ease this burden.”

Breast cancer is not a single disease, but a combination of distinct disease subtypes with varying risk factors and clinical outcomes. However, the reasons for differences in breast cancer biology and disparities in incidence and mortality rates between white women and african-american women are not well understood, and existing studies have not been large enough to provide sufficient statistical power to determine how and why breast cancers develop. The size and power of this new study could help address the current lack of scientific understanding.

This study will seek to identify novel genes and gene pathways which will significantly improve knowledge of breast cancer biology, particularly for african-american women.

The multicenter study will pool data, biospecimens, and expertise from 18 previous studies of breast cancer among women of african ancestry.  The investigators will determine whether genetic variants may be associated with increased risk. Specifically, they will examine:

  • The association between genetic variants and the risk of estrogen receptor-negative breast cancer and estrogen receptor-positive breast cancers
  • How genetic variants affect major breast cancer biological pathways and whether the effects may differ between african-american women and white women

In addition to researchers from VICC, Boston University and the University of Southern California, experts from 10 other institutions will gather information and biospecimens from 20,000 breast cancer cases.

Other VICC investigators include Jirong Long, Ph.D., Qiuyin Cai, M.D., Ph.D., Bill Blot, Ph.D., Bingshan Li, M.D., Ph.D., Carlos arteaga, M.D., and Thomas Stricker, M.D., Ph.D.

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We describe breast cancer incidence and mortality in the predominantly african-origin population of Barbados, which shares an ancestral origin with african-americans. age-standardized incidence rates were calculated from histologically confirmed breast cancer cases identified during a 45-month period (July 2002–March 2006). Mortality rates were estimated from death registrations over 10-years starting January 1995. There were 396 incident cases of breast cancer for an incidence rate of 78.1 (95% confidence interval (CI) 70.5–86.3), standardized to the US population. Breast cancer incidence in african-americans between 2000 and 2004 was 143.7 (142.0–145.5) per 100,000. Incidence peaked at 226.6 (174.5–289.4) per 100,000 among Barbadian women aged 50–54 years, and declined thereafter, a pattern in marked contrast to trends in african-american women, whose rates continued to increase to a peak of 483.5 per 100,000 in those aged 75–79 years. Incidence rate ratios comparing Barbadian and african-american women showed no statistically significant differences among women aged ≤39 years, marginal statistical differences among women 40–54 years and strongly significant differences among women aged ≥ 55 years (p ≤ 0.001 at all older ages). The age-standardized mortality rate in Barbados was 32.9 (29.9–36.0) per 100,000; similar to reported US rates. The pattern of diverging breast cancer incidence between Barbadian and african-american women may suggest a greater contribution from genetic factors in younger women, and from environmental factors in older women. Studies in intermediate risk populations, such as Barbados, may assist the understanding of racial disparities in breast cancer.