SAN ANTONIO -- Some women with 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 medicines, doctors reported Friday.

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 very sick 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 Dr. Jennifer Litton, a breast cancer specialist at the University of Texas M.D. Anderson Cancer Center.

She had no role in any of the studies, which were reported Friday 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. If the first one fails, the second one does the job," said Dr. Kimberly Blackwell of Duke University. She led the combo treatment study and has consulted for its sponsor, British-based GlaxoSmithKline PLC, which makes Tykerb, and for Genentech, which makes Herceptin.

One woman on the combo in the study suffered a fatal blood clot. The only other common, 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.