LOS ANGELES — Treatment for advanced breast cancer could improve significantly if doctors give women combinations of medications that attack tumors in different ways, two large clinical trials suggest.

In one study, researchers found patients fared better when a breast-cancer drug called an aromatase inhibitor was combined with another medication, Afinitor, which is used to treat kidney cancer but is not yet approved for breast cancer.

In the second study, two standard medications for women with a type of breast cancer known as HER2-positive were more effective when the investigational drug pertuzumab was added to the regimen.

The findings, reported Wednesday at the annual San Antonio Breast Cancer Symposium, point to a new paradigm in treating advanced breast cancer, a field that has not seen significant progress in recent years, cancer specialists said.

The studies signal that advanced breast cancer may be best treated with a strategic combination of targeted medications that wage war on the cancer along several biological pathways.

"These are two terrific new options. They are laying out a map on the way forward for breast cancer," said Dr. Jose Baselga, a professor of medication at Harvard Medical School who was involved in both trials. "The way forward is by doing smart combination therapies."

The approach in many ways mimics that used in treating those infected by HIV: Just as treatment with multiple drugs cuts the chance that the virus can develop resistance, attacking the cancer cells on multiple fronts reduces the chance that the tumors can mutate to thwart the assault against them.

In a large international study, an experimental drug from Genentech called pertuzumab held cancer at bay for a median of 18 months when given with standard treatment, versus 12 months for "You don't see that very often. ... It's a spectacular result," said one study leader, Dr. Sandra Swain, medical director of Washington Hospital Center's cancer institute.

Scientists cautioned that the data so far show only that the patients survived longer before their tumor advanced in size. They have not shown that survival rates are lengthened as well.

The report comes a few weeks after federal approval was revoked for another Genentech drug, Avastin, that did not meaningfully help breast-cancer patients. It still is sold for other tumor types.

The new drugs are some of the first major developments since Herceptin came out in 1998. It has become standard treatment for a certain type of breast cancer.

The new drugs are likely to be very expensive — up to $10,000 a month — and so far have not proved to be cures. Doctors hope they might be when given to women with early-stage cancers when cure is possible, rather than the very advanced cases treated in these studies.

Even short of a cure, about 40,000 U.S. women each year have cancer that spreads beyond the breast, and treatment can make a big difference in their lives.