Tests for genes don't predict breast cancer better

Studying genes linked to breast cancer may someday lead to better treatments, but they do little to improve a doctor's ability to predict who is likely to develop a tumor, researchers reported on Wednesday.

Their study in the New England Journal of Medicine found that testing for 10 errant bits of genetic code linked to breast cancer was no better for screening than asking old-fashioned questions involving a woman's conventional risk factors. These include family history, age of fertility and age when a first child was born.

Only when these questions were combined with genetic testing did the ability to predict a tumor improve. "It was not enough improvement to matter for the great majority of women," team leader Sholom Wacholder of the National Cancer Institute in Bethesda, Maryland, said in a statement.

The 10 mutations "are not ready to be a kit you can use to make your personal decisions by," NCI's Patricia Hartge, who worked on the study, said in a telephone interview.

The study did not look at the BRCA-1 and BRCA-2 breast cancer genes already used to assess cancer risk. Those genes are uncommon but when women have mutated versions they confer a high risk.

The 10 mutations studied are far more common, found in 20 to 40 percent of the population, but each one only seems to increase the risk by a small amount, said Hartge. They are single-letter changes in the genetic code called single-nucleotide polymorphisms or "SNPs".

After looking at the cases of 11,588 women age 50 to 79, nearly half of whom had been diagnosed with breast cancer, they discovered that testing for the mutations was only slightly better than assessing traditional risk factors.

In addition, among the women whose assessed risk of breast cancer changed as a result of the new test, it did not change enough to affect the way doctors would treat them.

In a commentary, Peter Devilee of Leiden University Medical Center and Matti Rookus of the Netherlands Cancer Institute said it is clear that the 10 breast cancer genes used in the test "are no more than the tip of the iceberg" when it comes to causing cancer.

"For women seeking advice on their personal risk of breast cancer, it is obviously too early to incorporate SNP testing into a counseling procedure, although such tests are already advertised for this purpose on the Internet," Devilee and Rookus said.

They predicted that will change over the next decade.

The real value of the 10 defects is that one of them might help researchers better understand the cause of breast cancer and lead to better ways to treat it, said Hartge.

"These are 10 new huge clues we didn't know before to get in and learn what fundamentally causes breast cancer."

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