Abstract SY42-03: Lifestyle factors and risk of aggressive forms of breast cancer among African American women.
Authors: Ambrosone Christine B. 
Published: August 2014

It has been known for decades that American women of African ancestry (AA) with breast cancer have worse overall and disease-free survival than those of European (EA) descent. For many years, it was presumed that this poorer survival was due to factors associated with socio-economic status, such as less access to care and screening, resulting in later stage disease. There has also been research investigating if lack of receipt of optimal treatment, other co-morbid conditions or patient characteristics could account, in part, for this higher mortality. However, it is now generally accepted that AA women tend to be diagnosed with tumors with more aggressive characteristics, including less differentiated high-grade tumors, and lack of expression of estrogen (ER) and progesterone (PR) receptors. AA women are also more likely to be diagnosed with basal-like breast cancers, identified through gene expression profiling and validated with immunohistochemical markers, and to be diagnosed with breast cancer at a younger age than EAs. There are no facile reasons to explain these differences in breast cancer epidemiology between AAs and EAs, and a number of genome-wide association studies (GWAS) have not identified genetic variants that appear to explain a large portion of this increased incidence of aggressive tumors in AA women.

The identification of breast cancer subtypes has enabled research to examine risk factors for more aggressive tumors in large cohort or case-control studies. The Carolina Breast Cancer Study (CBCS), led by Dr. Robert Millikan, was the first to categorize tumors by intrinsic subtypes and examine associations with traditional risk factors, with some surprising results. Although the standard risk factors for breast cancer include no or few children, those data were derived from studies of primarily EA women, the majority of whom likely had ER positive breast cancer. When Millikan and colleagues assessed parity and risk stratified by breast cancer subtype, they found, as expected, that having children reduced risk of luminal A breast cancer (ER, PR positive, HER2 negative), most common in older white women, but for basal-like breast cancer (ER, PR, HER2 negative, positive for cy5/6 and EGFR), having children actually was associated with a two-fold increase in risk. Importantly, breastfeeding totally ameliorated this increased risk of aggressive breast cancer. Since that initial paper in 2008, these findings have been replicated in a number of studies, including the Black Women's Health Study, a prospective cohort led by Drs. Julie Palmer and Lynn Rosenberg. Associations have also been observed in EA women. However, because AA women generally have higher parity, and are less likely to breastfeed, these lifestyle factors could, in part, play a role in the higher prevalence of aggressive breast tumors in AA women.

In this presentation, the literature on associations between other lifestyle factors and risk of aggressive breast cancer in AA women will be reviewed, and new hypotheses and ongoing research will be discussed.

Citation Format: Christine B. Ambrosone. Lifestyle factors and risk of aggressive forms of breast cancer among African American women. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr SY42-03. doi:10.1158/1538-7445.AM2013-SY42-03