WASHINGTON, D.C. - A new study that will look at 50,000 sisters of women diagnosed with breast cancer opened today for enrollment across the United States. The Sister Study, conducted by the National Institute of Environmental Health Sciences (http://www.niehs.nih.gov) (NIEHS), part of the National Institutes of Health (http://www.nih.gov) , will investigate environmental and genetic causes of breast cancer. The Sister Study is the largest study of its kind to look at breast cancer risk factors.

Women of all backgrounds and ethnic groups are eligible for the study if they are between the ages of 35 and 74; live in the United States; have never had breast cancer themselves; and have a sister-living or deceased-who has had breast cancer. To recruit a diverse group of volunteers and to ensure the results benefit all women, researchers are especially encouraging African-American, Latina, Native American, and Asian women, as well as women 60 and older, to join the Sister Study.

Sisters may be the key to unlocking breast cancer risk mysteries. Dale Sandler, Ph.D., Chief of the Epidemiology Branch at NIEHS and principal investigator of the Sister Study said, "By studying sisters, who share the same genes, often had similar experiences and environments, and are at twice the risk of developing breast cancer, we have a better chance of learning what causes this disease. That is why joining the Sister Study is so important."

At the beginning, volunteers will complete several questionnaires and provide a sample of their blood, urine, toenails, and household dust. "With that, we'll be able to look at how genes, activities of daily life, and exposure to different things in our environment are related to breast cancer risk," Dr. Sandler explained.

"We've made the process as easy and as convenient as possible, so we will come to you," she added.The landmark study will stay in touch with the volunteers for 10 years and compare those who develop breast cancer with the majority who do not. While past studies have largely focused on hormones, reproductive health, and lifestyle, the Sister Study will take the most detailed look ever at how women's genes, and things women come in contact with at home, at work, and in the community may influence breast cancer risk. Researches will study a range of environmental exposures, from personal care and household products, to workplace and other common exposures.

"Genes are important, but they don't explain it all," said Dr. Sandler. "The truth is that only half of breast cancer cases can be attributed to known factors." And, two known genes linked to breast cancer -- BRCA 1 and BRCA 2 -- play a role in only five to 10 percent of cases.

Women who may have felt helpless as they watched their sisters battle breast cancer now have an opportunity to help researchers learn more about causes of the disease. Dottie Sterling and Fluffy Reed both joined the study at the request of their youngest sister, Wish Martin, a breast cancer survivor in Maryland. "Throughout my sister's fight with breast cancer, we all prayed and prayed for healing and a swift recovery," said Sterling, a Sister Study volunteer in Ohio. "Now my sister has been a breast cancer survivor for more than 13 years, and I could not be more proud. I see joining the Sister Study as my tribute to her strength and her faith."

Many women have lost their sisters to breast cancer. "We need to find a cure for breast cancer and improve detection, diagnosis and treatment," said Patricia Bango, a participant in Virginia. "I joined the Sister Study as an advocate for my sister, Sally, who did not survive this devastating disease. I know her hope would have been that these efforts will help researchers find out what causes breast cancer."

The Sister Study opened in pilot states, including Arizona, Florida, Illinois, Missouri, North Carolina, Ohio, Rhode Island, and Virginia, earlier in 2004 but is now open for nationwide enrollment.Organizations that are in partnership with the Sister Study include the American Cancer Society, Sisters Network, Inc., the Susan G. Komen Breast Cancer Foundation, and the Y-ME National Breast Cancer Organization, as well as countless local community breast cancer support and advocacy groups. To volunteer or learn more about the Sister Study, visit the web site (http://www.sisterstudy.org) or call toll free 1-877-4SISTER (877-474-7837). Deaf/Hard of Hearing call 1-866-TTY-4SIS (866-889-4747).