The Sister Study: Genetic and Environmental Risk Factors for Breast Cancer
Condition: Breast Cancer
MeSH terms: Breast Neoplasms
Study type: Observational

Summary: 
      The Sister Study is prospectively examining environmental and familial risk factors for
      breast cancer and other diseases in a cohort of 50,884 sisters of women who have had breast
      cancer. Such sisters have about twice the risk of developing breast cancer as other women.
    

Detailed description: 
      The Sister Study is prospectively examining environmental and familial risk factors for
      breast cancer and other diseases in a cohort of 50,884 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 enhances our ability to understand the interplay of genes and environment in breast
      cancer risk and to identify potentially preventable risk factors. We assess exposures before
      the onset of disease, thus avoiding biases common to retrospective studies. The assembled
      cohort has created a framework from which to test new hypotheses as they emerge.

      Cancer-free sisters aged 35-74 were recruited nationally. Enrollment was completed July 2009
      with 50,884 women fully enrolled. Participants have enrolled from all 50 states and Puerto
      Rico. The cohort is now being followed actively. Cohort members are occasionally invited to
      participate in add-on studies, which sometimes include asking participants to invite their
      family members to provide information.

      Data on potential risk factors and current health status were collected with telephone
      interviews and self-completed questionnaires. Blood, urine, and environmental samples were
      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 is being followed prospectively
      for 10 or more years. Annual questionnaires update medical history and changes in exposures.
      About 300 new cases of breast cancer are expected to occur in the cohort each year. Analyses
      are ongoing and 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. Women who
      develop breast cancer during the study are followed to assess the role of environment and
      genes in healthy survival following diagnosis and treatment. 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.
    

Time perspective: Prospective
Keywords: Breast Cancer; Sisters