Sister Study

Lead Contacts and/or Principal Investigators (PIs):

  • Dale Sandler, Ph.D.
    National Institute of Environmental Health Sciences

Staff Scientist

  • Katie O'Brien, Ph.D.
    National Institute of Environmental Health Sciences

Funded Since: 2001
Funding Source: NIEHS Intramural Program with support from the National Center for Research on Minority Health and Health Disparities; Two Sister Study funded in part by Susan G. Komen for the Cure
Year(s) of Enrollment: 2003 to 2009
Study Website: http://www.sisterstudy.orgExternal Web Site Policy

The Sister Study, conducted by the National Institute of Environmental Health Sciences (NIEHS), is prospectively examining environmental and familial risk factors for breast cancer and other outcomes in a cohort of 50,884 sisters of women who have had breast cancer. These sisters have about twice the risk of developing breast cancer due to their family history and are expected to be highly motivated to participate in a long-term study. The frequency of any relevant genes and shared risk factors will also be higher, increasing the statistical power of the study to assess gene and environment interactions. Women who develop breast cancer while in the Sister Study will continue to be followed to assess the influence of environment and genes on treatment outcomes and long-term survival.

Breast cancer-free sisters aged 35 to 74 years were recruited from all states and Puerto Rico through health professionals, breast cancer advocates, the Internet, recruitment volunteers, and a national media campaign with an emphasis on recruiting under-represented groups. Study materials were available in English or Spanish. Data on potential risk factors and health status were collected in telephone interviews and mail questionnaires (Diet, Family History, and Personal Care Products). Baseline questionnaires on environmental, occupational, lifestyle, and health factors cover the lifespan — from in-utero exposures through reproductive years to the present. Blood, urine, and environmental samples were collected in a home visit and banked for future use in nested studies. Stored samples include whole blood, cryopreserved lymphocytes (15% random sample), plasma, serum, urine, toenail clippings, and household dust collected with alcohol wipes.

The cohort is being followed prospectively for ten or more years. Annual updates and tri-annual questionnaires provide information on changes in vital status, medical history and exposures. Medical records, pathology reports, and tumor tissue are sought for those who develop cancer. Medical records also are sought to confirm other health outcomes.

The Sister Study opened nationally in October 2004 after a pilot phase that began in August 2003. Enrollment was closed March 2009, with 50,844 women completing all baseline activities by August 2009. The majority of women have completed at least one annual update (as of April 2010) and the first detailed follow questionnaires (Health and Medical History, Lifestyle, and Stress and Coping) have been completed by about 30,000 women to date.

A related effort, the Two Sister Study, is enrolling affected sisters diagnosed before age 50 and within 3 years of the unaffected sister’s enrollment in the Sister Study. Parents of these sister pairs are also invited to contribute saliva samples for DNA to be used in family-based analyses.

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