'Landmark'?: US Blacks' Breast Cancer May Have African Roots

Kate O'Rourke

March 07, 2016

BOSTON — It is a troubling clinical fact that African American women are at higher risk for harder-to-treat breast cancers than other populations of women in the United States.

But investigating the possible role of genetics in that heightened risk has been complex because African Americans are an ancestrally mixed population, according to an international team of researchers.

So the team undertook a unique study that compared rates of breast cancer types among African American and white women in the United States as well as African women, both from East Africa and West Africa; the latter group is key because African Americans are known to have their roots in West Africa.

"Our results suggest that West African ancestry is associated with a hereditary susceptibility [among black Americans] for triple-negative breast cancer [TNBC]," said lead author Lisa Newman, MD, MPH, director of the Breast Cancer Program, Henry Ford Health System, Detroit, Michigan.

Triple-negative tumors test negative for estrogen, progesterone, and HER2 receptors and therefore are not targetable with standard therapies, such as tamoxifen (multiple brands) and trastuzumab (Herceptin, Roche). They are associated with a worse prognosis than other major types of breast cancer.

Dr Newman presented the study here at the Society of Surgical Oncology (SSO) 2016 Cancer Symposium.

Before explaining the study design and results, she provided some context for the study.

African American women bear a disproportionately high share of breast cancer mortality in the United States, she said. "The outcome disparity is partly explained by socioeconomic disadvantages that are more prevalent in the African American community, resulting in healthcare access barriers and diagnostic as well as therapeutic delays," commented Dr Newman.

"However, there are several features characterizing the epidemiology of breast cancer in African American women that cannot be easily ascribed to socioeconomic inequities," she continued. For example, African Americans are diagnosed with breast cancer at a younger age, and, until very recently, the lifetime incidence rates of breast cancer have been lower in African Americans than in whites.

Furthermore, the rates of TNBC are approximately twofold higher for the African American community compared with non-Hispanic whites and Hispanics, she noted, citing a recent study (J Natl Cancer Inst. 2015;107:djv048).

So Dr Newman and colleagues evaluated breast cancer phenotype and African ancestry by evaluating tumors from four different patient populations: African Americans (n = 321), white Americans (n = 272), Ghanaians, representing West Africa (n = 234), and Ethiopians, representing East Africa (n = 94) (P < .001).

The investigators found that individuals with African ancestry were younger at diagnosis; the median age was 43 years in the Ethiopian population, 49 years in the Ghanaian population, 60 years in African Americans, and 62 years in white Americans.

Furthermore, approximately half of the women with African ancestry, both in the United States and abroad, had high-grade tumors, compared with only one third of the white American patients, said Dr Newman.

Women with African ancestry also had higher rates of TNBC and estrogen receptor–negative tumors. The researchers noted that TNBC and estrogen receptor–negative tumors were more common in the African American and Ghanaian (West Africa) populations than in Ethiopians (East Africa).

Table. Phenotype Distribution

  White American African American Ethiopian Ghanaian
Estrogen receptor–negative, % 19.8 37.1 28.7 67.5
Triple-negative, % 15.5 29.8 15.0 53.2

 

"In trying to explain these patterns, we looked at patterns of forced population migration through the slave trade from several centuries ago," said Dr Newman.

She explained that African Americans share ancestry with sub-Saharan Western African women, such as those from Ghana, because of the patterns of the transatlantic slave trade.

On the other hand, African Americans probably have little shared ancestry with Ethiopians, because the East African slave trade was controlled by the Arabs and mainly went to Asia, she said.

A subset analysis based on age identified the same phenotype distribution for African American patients younger than 50 years.

"These data suggest that West African ancestry is indeed associated with some hereditary susceptibility to triple-negative breast cancer," said Dr Newman. She looks forward to future research involving larger patient populations and ancestry-informative markers.

Daniel Coit, MD, a surgical oncologist at Memorial Sloan Kettering Cancer Center, New York City, said the study was important.

"I think we will look back on this as a landmark abstract," said Dr Coit. "I suspect this is the beginning of a very strong collaboration between the SSO and international outreach to help establish these tissue repositories to try to figure this out."

Dr Newman and Dr Coit have disclosed no relevant financial relationships.

Society of Surgical Oncology (SSO) 2016 Cancer Symposium: Abstract 8, presented March 4, 2016.

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