Gene researchers find linkage to breast cancer

September 15, 1994|By Los Angeles Times

Utah researchers have identified the defective gene believed to cause about half of all inherited cases of breast cancer, a discovery that should make it possible within a year to identify the estimated 600,000 U.S. women who carry the gene.

These women have an 85 percent risk of developing breast cancer by age 65 and an unusually high risk of developing ovarian cancer. Identifying the women at risk could save many lives by allowing intensive monitoring and early detection of the tumors, which substantially increases the cure rate.

The discovery is the result of a massive effort triggered in 1990, when geneticist Mary-Claire King of the University of California, Berkeley, showed that the gene, commonly called BRCA1, is located on a small region of chromosome 17, one of the 23 pairs of chromosomes that contain every person's genetic blueprint.

The race to locate the gene was ultimately won by a team of more than 45 scientists headed by geneticist Mark H. Skolnick of the University of Utah and Myriad Genetics Inc. of Salt Lake City.

Another team has also identified the approximate location of a second gene, BRCA2, that is believed responsible for most of the remaining cases of inherited breast cancer in women, possibly many sporadic breast cancers.

The discover of BRCA1 is a "major advance [that] will enable us to identify women, particularly younger women, who have an increased risk of developing breast cancer," said molecular biologist Harold Varmus, director of the National Institutes of Health.

Perhaps even more important, however, will be the new understanding the genes provide about how breast cancer occurs, said Dr. Harmon Eyre, chief medical officer of the American Cancer Society.

"We actually know very little about what causes breast cancer," Dr. Eyre said. "This is a real first step in getting to the bottom of what it is all about."

Breast cancer activists were delighted, particularly because of potential implications for understanding the biology of the disease, said Michelle Rakoff, co-chair of the Los Angeles Breast Cancer Alliance. "What we have now is early detection," she said. "What we really want is prevention, and for that we need to know what causes it."

The three reports were scheduled to be published next month in the journal Science, but they were released yesterday after NBC News disclosed their contents.

Breast cancer is the most common form of cancer in women, striking an estimated 182,000 U.S. women and 1,000 men each year.

Researchers have known for more than 100 years that breast cancer runs in families, with this form of the disease accounting for about 5 percent of all cases. The inherited form is physically indistinguishable from sporadic breast cancer, but it strikes at an earlier age, with a large proportion of cases occurring in women under the age of 30.

Previous studies of more than 200 families with the BRCA1 gene have revealed that the gene is linked not only to breast and ovarian cancer, but perhaps to colon and prostate cancer as well. Both women and men in these families have an above-normal rate of colon cancer and men have an excessive amount of prostate cancer.

Mr. Skolnick said it would require at least a year to develop a test for the defective gene. A test to detect its presence could cost as much as $1,000, he added.

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