Avis Antel

In October of 2004, a new study looking at 50,000 sisters of women diagnosed with breast cancer opened for enrolment across the United States. The Sister Study, conducted by the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health, will investigate environmental and genetic causes of breast cancer. It is open only to residents of the United States.

This will be the largest study of its kind to look at environmental and genetic causes of breast cancer. Sisters may be the key to unlocking breast cancer risk mysteries because they share genes and at least some elements of lifestyle. Scientists already know that if a woman has breast cancer, her sister has a much higher chance of developing the disease, too. Dale Sandler, Ph.D., Chief of the Epidemiology Branch at NIEHS and principal investigator of the Sister Study says, "By studying sisters who share the same genes, often have 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."

American women are eligible to participate if they are between 35 and 74 years old, and have a sister related by blood who has been diagnosed with breast cancer. As part of the study, researchers will collect information from study participants about their lifestyles, medical histories, jobs and environment: blood samples and specimens of urine, toenails and house dust will also be collected. The women in the study will complete questionnaires about their diet, family history and environmental exposures. "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.

The Sister Study is a long-term study that will follow the women for at least ten years and compare those who develop breast cancer with the majority who do not. "Genes are important, but they don't explain it all," according to Dr. Sandler, "The truth is that only half of breast cancer cases can be attributed to known factors." Two known genes linked to breast cancer — BRCA1 and BRCA 2 — play a role in only five to ten percent of cases.

While past studies have largely focused on hormones, reproductive health, and lifestyle, this 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. Researchers believe ingredients in many common products like gasoline, pesticides, paint remover, glue and plastic interfere in the role of hormones, possibly contributing to the development of breast cancer. But past studies have not been able to establish a strong link. Researchers in the Sister Study hope data gathered in this study will shed some light on the health effects of such exposure, combined with genetic and age-based risk factors.

A similar study is being conducted in the U.K. where a 50-year study of breast cancer was recently launched. Researchers there aim to recruit 100,000 British women aged from 18 to 79 who will be studied over the course of their lives for factors affecting their risk for breast cancer. Although the death rate from breast cancer has fallen in recent years, thanks to improved treatment, the incidence of the disease is rising. Scientists hope that this rising trend could be reversed if the causes of the disease were better understood.