New findings add to the evidence that genetic tests can help predict whether breast cancer will recur, giving valuable guidance to doctors and patients about whether potentially toxic chemotherapy will be useful or can safely be avoided, researchers said yesterday.

The findings, presented at a breast cancer conference in San Antonio and in a paper released by The New England Journal of Medicine, suggest that telltale genetic signatures of tumors will in time be used to tailor treatments to individual patients.

“It would probably make a difference in the treatment of tens of thousand of women,” said Dr. Robert C. Bast Jr., vice president at the M. D. Anderson Cancer Center in Houston and co-author of an accompanying editorial released by the journal.

But Dr. Bast added that the tests were still “a work in progress” and needed more study before they could be used routinely.

The tests address a quandary for patients with breast cancer. When tumors are detected early and removed surgically, many women undergo chemotherapy to lower the chance that the cancer will recur.

But for a vast majority of women, the cancer will not recur regardless of whether they receive chemotherapy. So they are exposed needlessly to the treatment, which can cause nausea, hair loss, vulnerability to infections and, more rarely, cardiac problems or leukemia. Doctors cannot now tell, however, which women need the chemotherapy.

“There’s a substantial portion who we either undertreat or overtreat because we don’t have adequate information on who will recur,” said Dr. Gary H. Lyman of the University of Rochester, who has reviewed 10 such experimental tests.

The new tests “enhance the ability to distinguish between low risk and high risk,” said Dr. Lyman, who was hired to do a cost benefit analysis for the maker of the test described in the paper released yesterday.

That test was developed by Genomic Health, a company in Redwood City, Calif. The test looks at the activity levels of 21 genes in tumor samples. It categorizes the cancers as being of low, intermediate or high risk of recurrence.

To validate the test, company scientists and academic collaborators from the National Surgical Adjuvant Breast and Bowel Project used samples from 668 women. Those women had taken part in a trial in the 1980’s, so it was already known whether their cancers had recurred.

Only 6.8 percent of the women rated by the test to be in the low-risk group suffered a recurrence outside the breast within 10 years, compared with 14.3 percent in the intermediate group and 30.5 percent in the high-risk group.

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