Researchers at the University of California, Berkeley, on the brink of identifying a gene for hereditary breast cancer, warn that its discovery will present profoundly troubling dilemmas for women found to be susceptible to the cancer.
They estimate that one in 200 women -- or 600,000 nationwide -- may carry a gene that gives them an 80 percent risk of getting breast cancer by age 65. When researchers identify that gene -- which could be within a year or two -- these women will confront some terrifying choices with no guarantee of full protection.
"As soon as this gene is cloned, it will be possible to screen the population as a whole," said Mary-Claire King, a geneticist at UC-Berkeley who published a report today in the Journal of the American Medical Association. As a result, she said, "There are a large number of women in America who very soon will confront an extremely large risk of breast cancer."
Although most breast cancer is not hereditary, finding a gene for the hereditary form could eventually help researchers identify and treat non-hereditary cases. Ms. King, who is nationally known for pioneering work in the hunt for the gene, said she thinks the genetic mutation for both forms of the disease may be similar.
She recommended a national registry to track high-risk women and preventive treatments.
Ms. King outlined the three main options for women who know they have inherited a high risk of breast cancer:
* Close medical follow-up, including a yearly mammogram and a physical examination every six months, accompanied by frequent breast self-exams. This may help early detection of breast cancer but is less accurate in younger women because their breasts are more dense. Hereditary breast cancer often develops in women in their 30s or 40s.
* Removing both breasts to prevent cancer. However, doctors aren't sure whether a double mastectomy eliminates the risk of breast cancer because small amounts of breast tissue susceptible to cancer may remain.
* Participating in research studies of tamoxifen, a drug that is known to prevent breast cancer recurrence but that causes significant side effects, including premature menopause. No one knows whether tamoxifen can prevent breast cancer in high-risk women.
Most breast cancer -- 90 to 95 percent of all cases -- is not inherited. But because breast cancer is so common, striking one woman in nine, the remaining 5 to 10 percent of hereditary cases add up to 600,000 women nationwide.
That is far more common than other diseases for which a gene already has been found, such as Huntington's disease, which affects about 25,000 Americans.