SAN ANTONIO - Some women with very advanced breast cancer may have a new treatment option. A combination of two drugs that more precisely target tumors significantly extended the lives of women who had stopped responding to other drugs, doctors said yesterday.

It was the first big test of combining Herceptin and Tykerb. In a study of 300 patients, women receiving both drugs lived nearly five months longer than those given Tykerb alone.

Doctors hope for an even bigger benefit in women with less advanced disease and were elated at this much improvement for women who were facing certain death.

"We don't see a lot that works in patients who have seen six prior therapies as they did in this trial, so that alone is exciting," said breast-cancer specialist Jennifer Litton of the University of Texas M. D. Anderson Cancer Center.

The good results are in stark contrast to two other studies that found no survival advantage from Avastin, a drug whose approval for breast-cancer patients was very controversial. Two infusions a month, as needed for this treatment, cost at least $30,000.

Considering Avastin's potential side effects - blood clots in the lungs, poor wound-healing, kidney problems - a survival benefit "would have made the cost of the drug less painful to take," Litton said.

She had no role in the studies, reported yesterday at the San Antonio Breast Cancer Symposium.

Herceptin and Tykerb aim at a protein called HER-2 that is made in abnormally large quantities in about one-fourth of all breast cancers. Herceptin blocks the protein on the cell's surface; Tykerb does it inside the cell.

"It's kind of like having a double brake on your tumor," said Kimberly Blackwell of Duke University. "If the first one fails, the second one does the job."

Blackwell led the combo-treatment study and has consulted for its sponsor, British-based GlaxoSmithKline P.L.C., which makes Tykerb, and for Genentech, maker of Herceptin and Avastin.

Women in the study had already received Herceptin alone or with various chemotherapy drugs and still were getting worse. They were randomly assigned to receive only Tykerb or both drugs, to see if the combo might be more effective.

The results likely underestimate the combo's true benefit because women on Tykerb alone were allowed to add Herceptin partway through the study if they continued to worsen, and many of them did, Blackwell said.

One woman on the combo in the study suffered a fatal blood clot. The only other serious side effect was diarrhea, which plagued 7 to 8 percent of each group.

Herceptin costs about $10,000 a month; Tykerb, $5,000 to $6,000.