Sisters study probes genes, breast cancer

WASHINGTON -- A new national study will investigate genetic and environmental causes of breast cancer by enrolling 50,000 sisters of women already diagnosed with the disease.

The Sister Study, conducted by the National Institute of Environmental Health Sciences, part of the National Institutes of Health, is the largest study of its kind.

"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," Dr. Dale Sandler, the study's principal investigator, said in a statement yesterday.

The sisters who volunteer will donate blood, urine, toenails -- even household dust -- to help uncover how daily rituals and routines, as well as genetics, factor into breast cancer risk.

"Genes are important, but they don't explain it all," said Sandler, chief of the epidemiology branch at the environmental health institute. "The truth is that only half of breast cancer cases can be attributed to known factors."

For instance, BRCA1 and BRCA2 are genes that normally limit cell growth. Women who inherit an altered version of either gene have a higher risk of getting breast or ovarian cancer. BRCA1 and BRCA2, however, are implicated in just 5 percent to 10 percent of breast cancer cases.

Breast cancer is the second most commonly diagnosed cancer in women, after skin cancer. About 215,990 US women will be diagnosed with breast cancer this year, according to the American Cancer Society. The disease will kill about 40,110 US women in 2004, according to the Centers for Disease Control and Prevention.

To be eligible for the study, women need to be between 35 and 74. Those who have not been diagnosed with breast cancer are eligible if a sister, living or dead, has had the disease. They will be tracked for 10 years.

The study began as a pilot in Arizona, Florida, Illinois, Missouri, North Carolina, Ohio, Rhode Island, and Virginia.

Cruz Mireles, 58, of Peoria, Ariz., joined after seeing a booth with study details at Komen Race for the Cure, an event she has done annually since her sister was diagnosed at 40.

"I would like to see breast cancer eradicated, hopefully in my daughter's lifetime," said Mireles, whose daughter is 34.