The Sister Study: Genetic and Environmental Risk Factors for Breast Cancer

The Sister Study 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 any relevant genes and shared risk factors will also be higher. Studying
sisters will enhance our ability to understand the interplay of genes and environment in
breast cancer risk and to identify potentially preventable risk factors. We will assess
exposures before the onset of disease, thus avoiding biases common to retrospective studies.
The study will create a framework from which to test new hypotheses as they emerge.

Cancer-free sisters aged 35-74 are being recruited nationally. A total of 29,000 enrolled
through October 2006; 21,000 more women are needed. The study aims to include a divers group
of women. Women of color, older women, and women who work in trades are especially
encouraged to enroll. Additional information about the study and how to enroll can be found
at www.sisterstudy.org.

Data on potential risk factors and current health status will be collected with telephone
interviews and self-completed questionnaires. Blood, urine, and environmental samples will
be collected and banked for future use in nested studies of women who develop breast cancer
(or other diseases) and a sample of those who don't. The cohort will be followed
prospectively for 10 or more years. Annual questionnaires will update medical history and
changes in exposures. About 300 new cases of breast cancer are expected to occur in the
cohort each year. Analyses 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, obesity) and
include measurement of phthalates, phytoestrogens, insulin, growth factors, micro-nutrients,
and genes. The cohort will also be used to explore risk for other diseases (e.g. heart
disease, osteoporosis, other hormonal cancers, and autoimmune diseases) that are important
for women.

Inclusion Criteria:

Women who are eligible for the Sister Study:

- Have a sister (living or deceased) who had breast cancer

- Ages 35-74

- Never had breast cancer themselves

- Live in the United States

The Sister Study is currently recruiting sisters of women diagnosed with breast cancer
nationwide.