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Stress is a common belief among breast cancer patients and the public to explain variation in breast cancer incidence. Epidemiological studies interrogating the relationship between stress and cancer have reported mixed results. The impact of the topic and the lack of consensus has sparked this review of the literature to investigate gaps in knowledge and identify areas of research. We first present a brief summary of the biopsychosocial model generally used to conduct research on stress. We then divide the overview of the literature into areas of research focus. These include the role of distressing life events in breast cancer incidence, the role of adverse childhood events in later breast cancer incidence, the importance of race and socioeconomic status (SES) as social determinants of breast cancer incidence, and the specific role of chronic stress in relation to breast cancer. For each topic, we discuss the potential of stress as a risk factor and possible intervention strategies that could reduce the effects of stress. We then identify further research questions to be probed to fill the gaps in knowledge. We conclude with a discussion of future research directions for stress research as it relates to breast cancer incidence.

Racial disparities in breast cancer present a vexing and complex challenge for public health. A diverse array of factors contributes to disparities in breast cancer incidence and outcomes, and, thus far, efforts to improve racial equity have yielded mixed results. Systems theory offers a model that is well-suited to addressing complex issues. In particular, the concept of a systemic leverage point offers a clue that may assist researchers, policymakers, and interventionists in formulating innovative and comprehensive approaches to eliminating racial disparities in breast cancer. Naming systemic racism as a fundamental cause of disparities, we use systems theory to identify residential segregation as a key leverage point and a driver of racial inequities across the social, economic, and environmental determinants of health. We call on researchers, policymakers, and interventionists to use a systems-informed, community-based participatory approach, aimed at harnessing the power of place, to engage directly with community stakeholders in coordinating efforts to prevent breast cancer, and work toward eliminating disparities in communities of color.

Racial and ethnic differences in breast cancer occur by race/ethnicity in both incidence and mortality rates. Women of lower socioeconomic status likewise have poorer outcomes. When race alone is considered, incidence rates in the United States are highest among White women (130.8 per 100,000), with Black women close behind (126.7 per 100,000). Incidence is lowest among Asian/Pacific Islander women, at 93.2 per 100,000. Mortality differences are more pronounced, with Black women 40% more likely to die from breast cancer than White women (28.4 per 100,000 and 20.3 per 100,000, respectively). Mortality rates for Asian/Pacific Islander women (11.5 per 100,000) are far lower than for Black and White women. When age is considered, additional differences between Black and White women appear, in part accounted for by types of breast cancer experienced. Women of other racial/ethnic groups and socioeconomic status have received less scientific attention. In this article, we provide a brief overview of the evidence for social determinants of breast cancer and argue that the current reliance on race over racism and ethnicity contributes to our inability to eliminate breast cancer disparities in the United States and elsewhere in the world. We suggest alternatives to the current approach to research in breast cancer disparities.

The International Cancer Research Partnership (ICRP[1]) is an alliance of governmental and charitable organizations from the USA, Canada, Europe, Australia and Japan funding regional, national and international cancer research grants and awards. One key activity of the partnership is a database of information about member’s funded grant projects (N>60,000 grants, from 80 members, totalling over $14 billion USD). Each project is coded to a Common Scientific Outline (CSO), a classification system of broad areas of cancer research. Breast cancer is the most common cancer in women worldwide, however, only about 5-10% of breast cancer is attributable to genetic predisposition,[2] and about one third of cases are attributable to known genetic or other risk factors. In 2013, the Interagency Breast Cancer and Environmental Research Coordinating Committee (IBCERCC)[3] recommended that funding organizations plan strategically to accelerate the pace of scientific research on breast cancer and the environment. Thus, the ICRP has developed a mechanism to track activity and trends in research into environmental influences on breast cancer, to provide a baseline for future assessment of progress. Methods: ICRP-funded grants related to environmental influences on breast cancer were queried from the ICRP database. We focused on three time points: awards that were active in 2006, 2008 or 2010. The search resulted in a pool of 11983 breast cancer-relevant awards that was narrowed further to 1107 awards of relevance using a combination of keyword searches and specific Common Scientific Outline (CSO) codes.[4] Relevant awards were then coded with the assistance of keywords and manual review, to one or more, of 6 categories of environmental research: Behavior-Lifestyle, Behavior-Tobacco exposure, Chemicals-Chemical pollutants, Chemicals-Exogenous hormones, General Infection-Microorganisms and Radiation. Results: Between 2006 and 2010, the numbers of active awards declined and funding levels also fell. Most of the funded research is focused on behavioral/lifestyle factors in breast cancer (e.g., diet, alcohol intake, and shift work patterns). Further analysis of the Behavioral/Lifestyle category reveals that the major area of activity is in the role of nutrition/alcohol in cancer, closely followed by the contribution of obesity and reproductive factors (age of menarche, parity etc.). Conclusion: We were able to utilize a CSO ‘filter’ to identify trends in funded grant projects related to the environment and breast cancer. The decline in numbers and research funding between 2006 and 2010 is concerning. As breast cancer incidence continues to increase, research efforts to understand the causes of increased incidence are essential. Further research investment in these areas may be required. [1] https://www.icrpartnership.org/index.cfm [2] http://www.niehs.nih.gov/health/assets/docs_a_e/environmental_factors_and_breast_cancer_risk_508.pdf [3] https://www.niehs.nih.gov/about/assets/docs/summary_of_recs_508.pdf (Accessed 28/2/14) [4] CSO areas 2.1, 2.3, 1.2, 2.4, 6.2 (Etiology, Basic Biology of cancer initiation, and surveillance). Citation Format: Marc S Hurlbert, Senaida Poole, Kari Wojtanik, Samantha Finstad, Lynne Davies. ICRP analysis: Environmental influences in breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P2-09-02.