(Bloomberg) — Genetic tests for breast cancer risk often look for DNA flaws that haven’t been reliably linked to the disease, a new report found, casting doubt on diagnostics that examine dozens of genes to calculate a patient’s susceptibility.

Only 11 genes have potential mutations shown to raise the chance of getting breast cancer, according to the article published Wednesday in the New England Journal of Medicine. Some genes included in tests by Illumina Inc. and other companies haven’t been conclusively tied to breast cancer risk, the report said.

The cost of analyzing DNA -- the molecule containing the body’s code for making proteins, cells and tissues -- has dropped precipitously, and companies have added breadth to genetic tests for breast cancer risk. Yet more may not necessarily be better, according to an international team of researchers led by Douglas Easton, a cancer epidemiologist at the University of Cambridge in the U.K.

“If you’re selling tests with 100 genes when only 10 are important, that’s not very helpful,” Easton said in a telephone interview.

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Having a defect in one of the BRCA genes may raise a woman’s risk of developing breast cancer by age 70 as much as eightfold. Large-scale studies have shown that nine other genes — PALB2, PTEN, TP53, CHEK2, ATM, NF1, STK11, CDH1 and NBN — probably raise risk of the disease to varying degrees.

“We found insufficient evidence to establish any other genes as conferring a predisposition for breast cancer and would caution against their use in the prediction of breast cancer risk,” the researchers said in the report.

94 genes

Illumina’s TruSight test looks for flaws in 94 genes to establish breast cancer risk. The San Diego-based company declined to comment. Of 12 genes included in Myriad Genetics Inc.’s myRisk breast cancer risk test, three aren’t included in the report’s list of genes linked to the disease.

“In general, the article validates our own high threshold for inclusion of genes in the myRisk Hereditary Cancer test,” Ron Rogers, a Myriad spokesman, said in an e-mail.

Fulgent Diagnostics’ breast cancer risk test includes 39 genes. Doctors and patients can tailor the panel to their own wishes, adding or subtracting genes that they think might be more or less relevant to their case, said Joe Roach, vice president of the closely held Temple City, California-based company. More often than not, customers elect to add genes to the panel, he said.

“I want the freedom as a physician or patient to add those genes,” Roach said in a telephone interview. “I don’t want any sort of censorship or filtering done by an agency that might have a smaller view than the rest of the world.”

Unknown links

Invitae Corp., based in San Francisco, offers a panel of seven genes that have all been firmly linked to breast cancer. Clinicians should still have the opportunity to order gene tests at their discretion to assess risk, said Randy Scott, the company’s chief executive officer.

Testing genes that haven’t been closely linked to breast cancer, and then reporting the results to patients, may give a false idea of risk, Easton said. Patients may take preventive action -- frequent mammograms or even surgery -- based on misleading results, he said.

“The technology has run ahead of the evidence,” Easton said. “The patient is confronted with information about genetic variants for which no one knows what interpretation to give.”

U.S. oversight

Most genetic tests aren’t required to be approved by the U.S. Food and Drug Administration. Laboratory testing in the U.S. is overseen by the Department of Health and Human Services, which checks to see that the tests are done properly but not whether they provide useful information to doctors and patients.

Establishing links between genes and disease of any kind, including cancer, is a work in progress, said Heidi Rehm, a Harvard Medical School pathologist who directs the Laboratory of Molecular Medicine at Partners HealthCare in Boston. There have been many claims of links between mutations and disease without the evidence to prove it, she said.

In a separate paper in the journal, Rehm reported on progress on an effort called ClinVar, a database that collects information about genetic mutations and disease from hospital laboratories. The goal is to create greater accuracy and consistency in the interpretation of genetic tests, she said.

Until more research has been done, laboratories and companies should stop reporting breast cancer risk from any genes outside the 11 that have been shown to have an impact, Easton said.

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Dozens of genes in breast cancer tests have tenuous link to risk

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