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

The Sister Study

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

Two Sister Study Cohort Status (PDF)












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