The National Institute of Environmental Health Sciences needs sisters -- 18,000 sisters to be exact -- to join the nation's largest research project aimed at pinpointing the causes of breast cancer.

The Sister Study ideally will enroll a total of 50,000 women whose sisters had breast cancer. Since the study launch in October 2004, 32,000 women have been recruited. But still more are needed.

The 10-year observational study requires very little time, is available in English and Spanish, and requires women to first answer questions about diet, jobs, hobbies, and breast cancer risk factors. Later, a female health professional collects small samples of blood, urine, nail clippings, and house dust for use in analysis of environment and genetics.

Women in the United States and Puerto Rico between the ages of 35 and 74 may be eligible for the study if their sisters -- living or deceased -- had breast cancer. The study participants must have never been diagnosed with breast cancer themselves.

The Sister Study, in partnership with the American Cancer Society, NIH's National Center on Minority Health and Health Disparities, Sisters Network Inc., the Susan G. Komen for the Cure, the Y-ME National Breast Cancer Organization, and the Intercultural Cancer Council, is confidential and safe. Women are never asked to take medications, visit medical locations, or make any changes to their habits, diet, or daily life. They are simply asked to join this effort so that the mystery of breast cancer can continiue to unfold.

To volunteer or learn more about the Sister Study, visit www.sisterstudy.org or www.estudiodehermanas.org. Or call (877) 474-7837 or (866) 889-4747 for the hearing-impaired.