Sister Study

Epidemiology Branch

The NIEHS Sister Study (http://www.sisterstudy.org/English/index1.htm) (Spanish (http://www.sisterstudy.org/Spanish/index1_spa.htm) ) will prospectively examine environmental and familial risk factors for breast cancer and other diseases in a cohort of 50,000 sisters of women who have had breast cancer. Such sisters have about twice the risk of developing breast cancer as other women. The frequency of relevant genes and shared risk factors will be greater among sisters, increasing the statistical power of the study to detect risks. Sisters should be highly motivated, and study leaders predict high response rates and compliance over time. Thus, studying sisters will enhance the researcher’s ability to assess the interplay of genes and environment in breast cancer risk and to identify potentially preventable risk factors. The prospective design will allow them to assess exposures before the onset of disease and avoid biases common to retrospective studies. The study—projected to last 10 or more years—will also allow them to examine a wide range of health outcomes of relevance to women, and to create a framework from which to test new hypotheses as they emerge.

Cancer-free sisters are being recruited nationally through health professionals, breast cancer advocates, the Internet, a network of trained recruitment volunteers and a national advertising campaign. Recruitment strategies are designed to maximize inclusion of minorities and high-risk women. Study materials are available in English and Spanish.  Study researchers will collect data on potential risk factors and current health status using computer assisted telephone interviews and mail questionnaires. The scientists will collect and bank blood, urine and environmental samples for future use in nested studies of women who develop breast cancer (or other diseases) compared with those who do not. Annual tracking and bi-annual questionnaires will update contact information, vital status, and changes in medical history and exposures. Researchers may retrieve medical records and tumor tissue, if feasible, for those who develop breast cancer or other diseases.

Analyses of incident cases will assess the independent and combined effects of environmental exposures and genetic polymorphisms that affect estrogen metabolism, DNA repair, and response to specific environmental exposures. Future analyses will focus on known and potential risk factors (e.g., smoking, occupational exposures, alcohol, diet and obesity) and include measurement or analysis of phthalates, phytoestrogens, metals, insulin, growth factors, vitamins and nutrients, and genes in blood and urine. Ancillary studies will investigate the risk for other diseases (e.g., heart disease, osteoporosis, other hormonal cancers, respiratory disease, and autoimmune diseases) and explore genetic and environmental effects on breast cancer prognosis by continuing to follow women in the cohort who develop breast cancer.

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