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WEDNESDAY, Aug. 18 (HealthDayNews) -- A new blood test holds promise for improving the treatment of advanced breast cancer, researchers report.

The test, which looks for malignant cells in the blood, gives a quick read on how well women are responding to treatment for metastatic breast cancer, in which the malignancy has spread to other parts of the body, says a report in the Aug. 19 issue of the New England Journal of Medicine.

"When a woman starts one of several treatments, all of which are designed to shrink the tumor and make people feel better, this test can tell in a few weeks whether the therapy will benefit her," said Dr. Daniel F. Hayes, one of the researchers. "If not, she should be taking a different therapy."

Use of the test is in the earliest stages, said Hayes, who is clinical director of the breast oncology program at the University of Michigan Comprehensive Cancer Center. The study was conducted at 20 centers and focused on whether test results could tell how well a therapy was working.

A total of 177 women were tested, with the cutoff line for the test set at five cancer cells per 7.5 milliliters of blood. The average survival time for women whose readings were higher than that level was 8.2 months, compared to more than 18 months for those with lower blood levels of cancer cells.

But showing that a treatment is not helping a woman is just a first step, Hayes said. "We still don't know whether, if a woman has these tumor cells, a switch to another therapy will help her," he said.

Breast cancer can be treated either with therapy aimed at reducing production of estrogen, a hormone that accelerates the growth of cancer cells, or chemotherapy, with drugs that kill cancer cells. In this trial, the blood test was more accurate in predicting response to hormonal therapy than chemotherapy, Hayes said.

But it does appear better than existing methods of evaluating the effectiveness of treatment, he said. The most basic method is to monitor the woman's condition carefully, Hayes said, with that evaluation occurring over a period of months. The new test gives information in four or five weeks, he said.

There are older blood tests that look for cancer-related proteins, but their results are too equivocal to be widely used, said study co-researcher Dr. G. Thomas Budd, director of the medical oncology breast cancer program at the Cleveland Clinic.

"I believe that this method is more robust and gives more useful information," Budd said.

A starting application of the test would be to "identify women who do not benefit from a treatment, so we can spare them the side effects," he said. "Then we would try to prove that changing the treatment improves survival or betters the quality of life."

Trials to determine whether a change of treatment based on the test will improve survival are in the planning stage, Budd said.

The test is done by a specialized machine recently approved by the U.S. Food and Drug Administration, Hayes said. The device is just becoming available at major cancer clinics, but a long-range hope is that results can be obtained by mailing blood samples to testing centers, he said.

The test is currently intended for just 10 percent to 20 percent of breast cancer patients whose disease has spread, Budd said, but it might someday be useful for monitoring women who have been treated successfully for breast cancer.

"We could perform a test periodically to determine whether the cancer has recurred," Budd explained.

More information

What you need to know about breast cancer is told by the National Cancer Institute.

(SOURCES: Daniel F. Hayes, M.D., clinical director, University of Michigan Comprehensive Cancer Center, Ann Arbor; G. Thomas Budd, M.D., director, medical oncology breast cancer program, Cleveland Clinic; Aug. 19, 2004, New England Journal of Medicine)

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