‘Sister Study ’ Looks at Genetic, Environmental Breast Cancer Links

RESEARCH TRIANGLE PARK, North Carolina—Researchers have begun the first phase of a long-term, prospective epidemiological study designed to determine the role of genetic, environmental, and lifestyle factors in increasing the risk of breast cancer and several other diseases. The Sister Study is the first long-term follow-up study specifically designed to look at hereditary and environmental risk factors for the disease. It seeks to enroll 50,000 cancer-free women in the United States between the ages of 35 and 74 who have a sister diagnosed with breast cancer.

"Our overall goal is to create a framework from which we, and others who might collaborate with us, can ask questions about the role of the external environment, which has not been studied very well in breast cancer risk," said co-principal investigator Dale Sandler, PhD.

Dr. Sandler is the acting chief of the Epidemiology Branch at the National Institute of Environmental Health Sciences (NIEHS). The institute is funding the project, which is expected to cost about $7 million a year. Clarice Weinberg, PhD, chief of NIEHS’s Biostatistics Branch, is the other co-principal investigator.

"The Sister Study is unique among cohort studies in the emphasis we have put on external environmental exposures," Dr. Sandler said. "The current cohort studies— the Nurses’ Health Study and others— really focus on lifestyle. In the Sister Study, we are trying to address this other piece of the puzzle, the environment."

Researchers began recruiting for the study in Tampa, Florida, in September and have expanded their efforts to Phoenix, Arizona; St. Louis, Missouri; and Providence, Rhode Island, all chosen for the initial phase of the study because of their size and geographic, ethnic, and socioeconomic diversity.

The target enrollment for the four cities is 2,000 women over 6 to 9 months. Using the experience they gain from enrolling women from the initial four cities, the research team will refine its recruiting strategies and launch a national enrollment effort in the summer of 2003.

Dr. Sandler and her colleagues have enlisted breast cancer advocates and other groups to aid in enrollment. The initial recruitment effort took place during the Tampa Bay area Race for the Cure. "We have built a list of volunteers who are connected with different organizations throughout the United States, who have agreed to help us recruit women," Dr. Sandler said.

The sister of a woman who develops breast cancer has up to double the risk of getting the disease herself. "This is due to a combination of their shared genetics and probably their shared environmental and lifestyle exposures," Dr. Sandler said. "They share their early lives, and they take many of their habits and diet with them into their separate adult lives."

Followed for at Least 10 Years

Participants in the Sister Study will be followed for at least 10 years in an effort to determine whether the increased risk for breast cancer lies in such things as shared genes, a common diet, early menstruation, a household or environmental chemical, and/or a gene-environment interaction. Researchers will also look for factors that might prevent breast cancer. During each year of the study, about 300 participants are expected to be diagnosed with the disease.

Although its primary focus is on breast cancer, the Sister Study will also investigate risk factors for ovarian and endometrial cancer, as well as cardiovascular disease, osteoporosis, autoimmune diseases, and thyroid diseases, Dr. Sandler said.

At the study’s outset, researchers will collect biological and environmental samples from the women—including blood, urine, toenail clippings, and dust from their homes—to measure certain chemicals, hormones, and environmental substances. The samples will be stored for later analyses. "As women develop breast cancer, we will analyze the samples and compare the results with those from the women who didn’t develop breast cancer," Dr. Sandler said.

Each woman will also answer a detailed questionnaire about her family history, lifestyle, diet, occupational history, residence, medical and reproductive history, and environmental exposures. Thereafter, each participant will answer a shorter questionnaire annually.

The Sister Study has few exclusion criteria. Women are eligible for the study whether or not their sister diagnosed with breast cancer is living or dead, or whether she is a full sister or half sister.

Beginning in December, the study will also enroll a limited number of women who have been diagnosed with breast cancer for the first time within the past 4 months and have an eligible sister without breast cancer.

The researchers expect the Sister Study to return statistically significant, long-term data. "We are studying a group of women who want to be studied," Dr. Sandler said. "These women are concerned about breast cancer because they have it in their family; they want to do something. We think that we are going to be able to do this very well, whereas other cohorts may have more difficulty in terms of compliance."

Additional information is available online at http://www.sisterstudy.org or by calling 1-877-474-7837.