Patty Farrell was crushed when her big sister, Eileen, was diagnosed with breast cancer at age 36.

Patty Farrell was crushed when her big sister, Eileen, was diagnosed with breast cancer at age 36.

It wasn't just concern for her sister, who died 10 years ago after a long struggle. Physicians know that a woman whose sister gets breast cancer is twice as likely to develop the disease as a woman from the general population.

The known breast cancer genes alone can't explain the doubled risk, and researchers are looking for other factors that might offer some explanation. So when a friend told Farrell about a study that tracks the sisters of women who have had breast cancer, she jumped at the chance to enroll.

"It's a way I could do something instead of just sitting around," the retired law enforcement investigator said.

Farrell joined thousands of women across the United States who have already volunteered for the Sister Study, a project designed to determine the role that genes and environmental factors play in breast cancer.

Sisters make an ideal study group, said Paula Juras, one of the researchers conducting the study for the National Institute of Environmental Health Sciences.

"Very often sisters have very similar early environments," Juras said in a telephone interview from North Carolina. "They grow up in the same home; they're exposed to the same substances.

"Even as adults they may use the same products or have similar environments," Juras said. "To be able to study and compare the women who get breast cancer and those who don't is a powerful way to study."

Women who are accepted for the study agree to share information about their life history, jobs and home environment.

"They go all the way back to when you were a kid," said Farrell, 55. "It made me really have to think. That's way back there.

"They went into such detail about where you lived, and your home," Farrell recalled. "I had to call my mom a couple of times (for answers)."

Juras said researchers are looking for living situations or work environments that might have exposed study participants to known or suspected carcinogens. Participants also provide blood and urine samples, dust samples from their homes and toenail clippings.

The samples give researchers information about participants' more recent exposure to toxic chemicals. Toenails are particularly useful because they grow slowly and tend to accumulate toxic metals. House dust can tell researchers about exposure to substances such as pesticides and phthalates, chemicals that are used in many personal care products and have been shown to alter hormone production in extremely minute concentrations.

The study is open to all women in the United States and Puerto Rico between the ages of 35 and 74 who have a sister who has been diagnosed with breast cancer. Participants must never have had breast cancer themselves. Juras said women ages 55 to 74 are especially encouraged to apply because post-menopausal breast cancer can be quite different from young-onset breast cancer.

Study coordinators hope eventually to recruit 50,000 women, who will provide a representative sample of the different ethnicities and age groups of women in the United States. As of mid-November, more than 40,000 women had already enrolled.

After the initial interview, researchers will stay in touch with participants once a year to maintain current address records. Otherwise, women just go on with their daily lives.

"We're not asking women to make any changes in their routines," Juras said.

Participants agree to inform the researchers if they have any health changes. If a participant develops breast cancer, researchers will request permission to contact treating physicians and obtain additional tissue samples. Participants can choose whether to grant the request.

Juras stressed that all survey information will be kept strictly confidential, and the study has been constructed to ensure maximum privacy.

"We have legal protections that prevent even the Supreme Court from getting our data," she said. "I want people to know it's safe to participate in this study."

Researchers will stay in contact with women for at least 10 years, longer if additional funding is secured. "The longer we stay in touch the more we'll be able to learn," Juras said.

Farrell believes in the Sister Study so much that she's become something of a recruiter. She carries brochures about the project in her car and gives them to women if the subject of breast cancer comes up. That happens all too often, given that one in every eight or nine women will develop breast cancer during her lifetime.

"If any of this information can help determine how the environment and our genes affect breast cancer, then heck, this is one of the easiest things you can do," she said.

"It takes very little time, and it could make a huge difference."

On the Web: www.sisterstudy.org. Reach reporter Bill Kettler at 776-4492 or e-mail bkettler@mailtribune.com.