A new test might allow some women with the earliest phase of breast cancer to forgo the most aggressive treatment, researchers are reporting this week.

The test analyzes gene activity in tissue surgically removed from women with ductal carcinoma in situ to predict how likely it is that cancer will come back. Those with the lowest risk of recurrence might be spared radiation treatment.

The developer of the test, the biotechnology company Genomic Health, already sells a widely used test, known as Oncotype DX, that predicts the chance of recurrence for certain types of early-stage invasive breast cancer. That allows some women deemed to have a low risk to skip chemotherapy.

The company now hopes to apply the same technique to ductal carcinoma in situ, a noninvasive lesion in the milk ducts. Results describing the accuracy of the new test will be presented Thursday at the San Antonio Breast Cancer Symposium.

There are about 45,000 cases diagnosed per year in the United States, almost all of them picked up by mammograms. There is controversy about whether these lesions should even be considered a form of cancer.

Still, most women have the lesion removed surgically, usually by lumpectomies, said Dr. Joseph A. Sparano, vice chairman of medical oncology at the Montefiore Einstein Center for Cancer Care in New York. About two-thirds of women who get a lumpectomy then receive radiation therapy, which can reduce the recurrence rate by about half, he said.

In the study being presented in San Antonio, the Genomic Health test was run on 327 samples of excised tissue left over from a clinical trial conducted by the National Cancer Institute years ago, in which women with what was considered low-risk D.C.I.S. had their lesions removed but were not given radiation therapy.

Since the trial was conducted years ago, it was already known whether the women had a recurrence. However, the people analyzing the samples were blinded to this.

Women whose samples got a score predicting low risk had a 5.1 percent chance of developing invasive breast cancer in the same breast over the next 10 years and a 12.0 percent chance of developing either invasive breast cancer or another case of D.C.I.S.

By contrast, those who had the highest risk scores had a 19.1 percent rate of invasive breast cancer and a 27.3 percent chance of either invasive breast cancer or D.C.I.S.

Such a test “could make patients more confident in the decision” to choose surgery alone, without radiation, said Dr. Sparano, who is an author of the study.

Since 75 percent of the samples were given a low-risk score, that could result in substantial savings. Radiation can cost $8,000 to more than $15,000 and has side effects including sores and burns and, in rare cases, heart or lung damage.

However, the test itself, which Genomic Health plans to start marketing at the end of this month, costs $4,175.

The new test and the Oncotype DX test for invasive breast cancer analyze the activity of the same 21 genes in the tumor sample. However, the tests compute the risk score differently.

One question is whether the difference between the outcomes for the low- and high-risk scores is big enough to really influence treatment decisions. Some women with a low risk score, for instance, might still want radiation because they view a 12 percent risk of recurrence as too high.

Some experts said another shortcoming is that there is no data on how much radiation treatment would help the women in the different risk categories. It is theoretically possible, for instance, that radiation would not reduce recurrence very much in the high-risk group.