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Your Environment. Your Health.

Sister Study or el Studio de Hermanas

Closed for Recruitment

Study / Trial Background

The Sister Study is conducted by the National Institute of Environmental Health Sciences, one of the National Institutes of Health, of the US Department of Health and Human Services. From 2004 to 2009, more than 50,000 women across the US and Puerto Rico, who were between ages 35–74 and whose sister had breast cancer, joined this landmark research effort to find causes of breast cancer. Because of their shared environment, genes, and experiences, studying sisters provides a greater chance of identifying risk factors that may help us find ways to prevent breast cancer.

The Sister Study is currently tracking the health of women in the cohort. Participants complete health updates each year, as well as detailed questionnaires about health and experiences every two-to-three years. Research in the Sister Study focuses on causes of breast cancer and other health issues in women, as well as on factors that influence quality of life and outcomes after a breast cancer diagnosis.

For more information on this study, please visit the Clinical Trials webpage for this study.


The study has completed enrollment.

  • Ages Eligible for Study: 35 Years to 74 Years
  • Genders Eligible for Study: Female
  • Accepts Healthy Volunteers: Yes 

Inclusion Criteria: 

Women who are eligible for the Sister Study: 

  1. Have a sister (living or deceased) who had breast cancer 
  2. Ages 35-74 
  3. Never had breast cancer themselves 
  4. Live in the United States 

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

What will you do?

Participants will be followed for at least 10 years. Every year, we will send you an Annual Health Update that you can use to record major changes in your health status (for example, a diagnosis of breast cancer, heart attack, etc.). We ask you to return it even if there have not been any changes to your health. If you develop any medical conditions, you may also let us know by calling us toll-free at 877-4SISTER (877-474-7837).

We will ask you to complete follow-up questionnaires every two to three years. The follow-up questionnaires or interview will let us update your health status in more detail than we can with the Annual Health Updates. The follow-up questionnaires will also allow us to ask questions that will address any new theories about breast cancer that may arise.

What will NIEHS do?

The information collected in the Sister Study will be used to identify risk factors that may increase the chances of developing breast cancer. The results will be reported in papers that will be published in scientific literature, including journals read by physicians, epidemiologists, and laboratory scientists. Results will also be reported in the national and regional press, and to the participants in newsletters and on the website. Published summary reports from the Sister Study will also be available to government and other organizations that make decisions about evidence that specific agents cause cancer or other diseases and to those who make policy recommendations. Also, these reports will be available to other investigators who may wish to test ways to prevent disease.

We will let you know what we learn by combining the results of tests from many women. We hope that our analyses will provide information that can be used to help women prevent breast cancer and we will make sure to share that information with you.

If, in the course of testing blood samples from many women in the study, we learn something that, in our judgment, is especially important to tell individual participants, we will work with our Institutional Review Board (the committee responsible for overseeing the quality of our research and the safety of research participants) to determine the best way to inform participants.

On a regular basis, we will send you newsletters with highlights of general study results. Results of the study will be published in scientific journals. A list of these published articles and links can be found on the Published Articles page of our website.

Study / Trial Location

NIEHS Clinical Research Unit (CRU) – Research Triangle Park, North Carolina, USA 27709

Protocol Number: 02-E-N-271

Enrollment and Contact Information

Additional information can be found at the Sister Study website.

Call toll-free 877-4SISTER

For deaf or hard of hearing, call:

Please use this form to send your question or comments to the Sister Study. Or if you like, e-mail us at; however, be mindful that we cannot protect your personal information sent through email.

Principal Investigator

Photo of Sandler, Dale P.
Dale Sandler, Ph.D.
Chief, Epidemiology Branch and Senior Investigator
Tel 984-287-3711
Fax 301-480-3290
P.O. Box 12233
Mail Drop A3-05
Durham, N.C. 27709
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