(CNN) -- Taken together, the preliminary results of five eagerly awaited studies suggest that breast cancer patients who receive high-dose chemotherapy followed by bone-marrow transplants have similar survival rates to those of patients who receive standard treatment.

A relatively small number of breast-cancer patients opt for high-dose chemotherapy. These patients usually have cancer that has spread to 10 or more lymph nodes or has metastasized to other parts of the body.

The American Society of Clinical Oncology (ASCO) released the preliminary results of the studies on the Internet Thursday morning. Many doctors and patients had hoped the new data would provide guidance on whether women should undergo potentially risky high-dose chemotherapy -- which requires bone-marrow transplant procedures along with it -- or stick with conventional, lower doses of chemotherapy.

But ASCO stresses it's still unclear whether women should have the higher-risk treatment. Its Web-site statement reads: "Given the preliminary nature of the data, the conflicting initial results, and the specific differences in the study designs, it is not yet possible to draw definitive conclusions about the role of high-dose chemotherapy in breast cancer."

Bone-marrow transplants, or a similar procedure called stem-cell transplants, have no therapeutic effects by themselves. They're important because they support patients receiving high-dose chemotherapy. Such large doses destroy bone marrow. The transplant, which may use the patient's own marrow or that donated by someone else, replaces what's been destroyed.

In four of the five studies, researchers found no statistically significant difference in survival rates between women who received high-dose chemotherapy and those who received standard therapy. The fifth study, which was relatively small, did suggest that the high-dose chemotherapy may work better.

In the largest study, conducted in Philadelphia with 874 women, those who received high-dose chemotherapy had a 68-percent chance of being alive three years later, compared to a 64-percent chance of survival for women receiving standard lower-dose therapy. In the subjects of this study, the cancer had spread to 10 or more lymph nodes.

The second-largest study, also in Philadelphia, was conducted with 553 women with metastatic breast cancer. After three years, women who received the high-dose treatment had a 32-percent survival rate, compared to a 38-percent survival rate for patients on standard treatment.

Similar results were found for studies in Scandinavia and France. One study, conducted in South Africa with 154 women, did show a difference in treatment. After more than five years of follow-up, mortality was 17 percent for the women who received the high-dose treatment, compared to 35 percent for women who received standard treatment.

William Peters, lead author of one of the Philadelphia studies, says that even though four of the five studies suggest that the two treatment approaches yield the same results, it's too early to conclude that high-dose chemotherapy is unnecessary. "We need more time," he said in a news conference Thursday morning. "It will take another three years to have adequate information to make any conclusions."

ASCO: 1999 Plenary Session Abstracts Plus

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