Washington — Studies linking abnormal genes to a high risk of breast cancer have led some women to have their breasts removed pre-emptively as a precaution. Now a new analysis of those studies suggests the role of genes in evaluating cancer risk may have been exaggerated.
Precautionary breast removal, called prophylactic mastectomy, has been performed for many women who have a high frequency of breast cancer in their family and who have mutations in the BRCA1 and BRCA2 genes. Such women are thought to have a lifetime breast cancer risk of 80 percent or more.
But Colin B. Begg of Memorial Sloan-Kettering Cancer Center in New York said this high risk rate cannot be applied to every woman with mutations of the BRCA genes.
"It is likely that the typical mutation carrier would have risks lower than that," said Begg, who wrote an analysis published this week in the Journal of the National Cancer Institute. "Relatively few mutation carriers would have risks that high."
Some experts acknowledge there probably have been women who chose to have their breasts removed based on data now known to be exaggerated.
Begg said early studies that evaluated breast cancer risk among gene mutation carriers selected women in families where sisters, mothers and grandmothers had breast cancer. This created a statistical bias that skewed risk estimates for women in the general population, he said.
"The risks that have been quoted are among the highest because they have been based on studies using high-risk families," Begg said in a telephone interview from France, where he was on vacation.
Later studies showed the breast cancer risk among mutation carriers "is highly variable," he said. "The average risks are lower than what has been quoted.
"We don't know at the moment how to predict risks well for the individual," he said.