Herceptin, the breast cancer drug developed by Genentech, reduces the risk of death for certain stomach cancer patients by 26 percent compared with chemotherapy alone, according to new research.

"This will quickly have an impact on the standard of care," said Dr. Richard Schilsky, president of the American Society of Clinical Oncology, which is holding its annual meeting here. "It's going to force us to test stomach cancer patients on whether they are HER-2 positive or not."

Herceptin, or trastuzumab, is currently approved for use in the 25 percent or so of breast cancer patients whose tumors generate a protein called HER-2, which can fuel cancer growth.

Genentech, now a unit of Roche Holding AG, said high amounts of the HER-2 receptor are also found in up to a quarter of patients with stomach cancer.

"This is the first phase III study to report improved overall survival with a personalized, targeted treatment for gastric cancer," said Dr. Eric Van Cutsem, professor at the University Hospital Gasthuisberg in Leuven, Belgium, and lead author of the study.

Median overall survival was 13.8 months in the Herceptin plus chemotherapy group compared with 11.1 months in the standard chemotherapy group.

Researchers said the treatment was generally well tolerated and there were no unexpected side effects. The rate of symptomatic congestive heart failure was similar between the two groups, they said.