Women do not automatically have a higher risk of getting breast cancer just because someone else in the family has tested positive for breast cancer genes, U.S. researchers said.
The findings may bring comfort to women from high-risk families after a 2007 study suggested that simply having a relative with a BRCA1 or BRCA2 mutation raised their risk of developing breast cancer, even if they had tested negative for the genes.
"The results are encouraging and reassuring," said Dr. Allison Kurian of Stanford University School of Medicine, whose study appears in the Journal of Clinical Oncology.
The average woman in the United States has about a 12 to 13 percent chance of developing breast cancer in her lifetime.
Some 5 percent to 10 percent of breast cancers are genetic, and most of these cases are caused by abnormalities in the BRCA1 or BRCA2 genes.
Women with these mutations have a five to 20 times higher risk of developing breast or ovarian cancer, and must undergo intensive cancer screenings and take other precautions to reduce their cancer risk.
Many of these women elect to have their breasts or ovaries removed to keep from developing cancer.
Once these mutations turn up in a family, other family members are screened as well. Women from these families who test negative have traditionally been told they have about the same risk as women in the general population.
But a 2007 study published in the Journal of Medical Genetics challenged that notion, suggesting that even though women did not carry the family breast cancer mutation, they still had a two to five times higher risk of developing breast cancer.
That created a considerable amount of anxiety among doctors and patients, Kurian said in a telephone interview.
They compared breast cancer rates among carriers and noncarriers of family mutations of the BRCA1 and BRCA2 genes.
They found no evidence of an increased breast cancer risk among women who were noncarriers.
"It's reassuring that we don't see a signal for elevated breast cancer risk from women who test negative for a familial mutation," Kurian said.