WASHINGTON — Eagerly anticipated research results released Wednesday indicate that two recently discovered "breast cancer genes" play a less important role in cancer than scientists had presumed.
Women who inherit faulty versions of the two genes, called BRCA1 and BRCA2, are less likely to get breast or ovarian cancer than previous studies had indicated, and the mutations are present in a smaller number of breast cancers than had been anticipated, according to the new work.
Experts said the findings complicate an already dauntingly complex picture of the role of genes in breast and ovarian cancer. Most immediately, they suggest that expensive tests for these genes, which have become increasingly available commercially, may have less medical value than had been believed for most women.
"At this time we cannot predict an individual's risk based on genetic testing alone," said Margaret A. Tucker, who with Jeffrey P. Struewing, both of the National Cancer Institute, led a Washington-based study of more than 5,000 people to assess the risk of cancer conferred by the two genes.
Scientists had hoped that the discovery a few years ago of the two cancer genes would quickly speed identification of women at risk and lead to earlier diagnoses and improved treatments. Instead, scientists said, the new report in today's New England Journal of Medicine highlights the need to discover additional risk factors.
The new numbers say that a woman who carries one of the key mutations in BRCA1 or BRCA2 but who does not a have a notable history of breast or ovarian cancer in her family has about a 50% chance of developing breast cancer by the time she turns 70. That's about four times higher than the 13% risk faced by U.S. women overall, but much lower than the 85% odds suggested by previous studies. Those studies had focused on women whose families had long histories of breast and ovarian cancer, and who are apparently not representative of most women.
Similarly, the risk of ovarian cancer in women carrying one of the key mutations is 16%, higher than the national average of 1.6% but far lower than previous estimates of 40%.
Researchers also found that men with a BRCA1 or BRCA2 mutation have a 16% chance of developing prostate cancer, compared with 3.8% in the general population.