National Institute of Environmental Health Sciences   —  National Institutes of Health   —  U.S. Department of Health and Human Services

The Sister Study

Working together to discover ways to prevent breast cancer.

Special studies

Two Sister Study

The Two Sister Study is an offshoot of the Sister Study that focuses on young-onset breast cancer and is based on families. The study, conducted by the National Institute of Environmental Health Sciences, was led by Drs. Clarice Weinberg, Dale Sandler, and Lisa DeRoo and funded in part by Susan G. Komen for the Cure. Risk factors for young-onset breast cancer differ from those for breast cancer occurring at older ages. Although breast cancer is uncommon below age 50, women who develop the disease at a young age can help us learn a lot about genetic and environmental causes. Women who were younger than 50 when they were diagnosed with breast cancer, were diagnosed recently, and had a sister enrolled in the Sister Study were invited to participate in the Two Sister Study, along with their parents. Over 1,400 young-onset sisters enrolled in the study by completing questionnaires and/or providing saliva samples for DNA, along with 1,700 of their sisters in the Sister Study. Of their parents, 1,438 provided a saliva sample. About 1,300 of the sisters with young-onset breast cancer completed all of the study requirements (all questionnaires and saliva sample) and are now being followed prospectively along with Sister Study participants who developed breast cancer after joining the study. Thus, not only is the Two Sister Study an opportunity to learn about the genetic and environmental causes of young-onset breast cancer, the study will also provide information to learn more about breast cancer survivors and factors that can promote their long-term health following treatment.

Two Sister Study Participant Geographic Distribution

Centers for Disease Control and Prevention (CDC) Surveys


In 2011, The Sister Study partnered with the Centers for Disease Control and Prevention to help advance EARLY Act goals. The EARLY Act is legislation passed by Congress in 2010 to advance the awareness and understanding of breast cancer in young women. As part of this effort, approximately 20,000 Sister Study participants completed a special survey on impact of breast cancer in families with questions on breast cancer screening, family communication about cancer, and how having a sister with breast cancer has affect them and their families.

A second special survey of breast cancer survivors launched in fall 2012 focuses on the quality of life and other areas of concern for women who have experienced breast cancer diagnosis and treatment. The large cohort of breast cancer survivors in the Sister and Two Sister Studies (approximately 3000 participants as of January 2013) were asked to provide information about their quality of life after cancer, work after cancer, barriers to healthy behaviors as a survivor, issues related to stress and coping with breast cancer, personal decision-making about medical care, and experiences with treatment-related side-effects. By including participants in from the Two Sister Study, it will be possible to address issues that are important to women who develop breast cancer at younger ages including workplace issues, fertility and accelerated menopause.


Mother's Validation Study

The goal of the Mother’s Validation study is to determine how well women in the Sister Study are able to answer questions about their birth, infancy and childhood experiences. The Mother’s Validation study, led by Dr. Aimee D’Aloisio in conjunction with Drs. Dale Sandler and Clarice Weinberg, invited a random sample of 3,555 Sister Study women to participate along with their mothers. The daughters were between the ages of 35 and 59 whose mother was alive at the time the she enrolled in the Sister Study. Mothers were asked to complete a questionnaire similar to those filled out by their daughters covering topics such as the mother’s pregnancy with the daughter, birthweight, the daughter’s early life exposures and childhood residence, and family history of disease. Nearly 70% of mothers completed the questionnaires after exclusions for mothers who were deceased or had a cognitive impairment reported by their daughter. The Mother’s Validation study will provide a better understanding of how well women report information about their birth and early life experiences which is important given that in utero and childhood exposures may influence health later in life.  


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