Avastin, sold by Roche, is approved as a first-line or second-line treatment for colorectal cancer, but not for both. Sales of the drug, also known as bevacizumab, totaled $5.3 billion Swiss francs ($5.5 billion) last year.

"By simply switching chemotherapy drugs when the cancer progresses and continuing with bevacizumab, we can make second-line treatment even more powerful," said Dr. Dirk Arnold, director of Germany's Hubertus Wald Tumor Center of University Cancer Center Hamburg, and a trial investigator.

First-line treatment is initial treatment, while second-line treatment occurs after cancer starts showing signs of progression.

Avastin is an antibody that blocks vascular endothelial growth factor, or VEGF, a protein tumors need to grow nutrient-providing blood vessels. It is approved in the United States for treating glioblastoma, colorectal, lung and kidney cancers.

"A fundamental feature and importance of this study is that it does confirm our hypothesis that continuing to inhibit VEGF throughout the lifetime of a tumor can reduce its growth and survival," said Sandra Horning, head of global development at Roche's Genentech unit.

The Phase III study involved 820 patients with metastatic, inoperable colorectal cancer who had been treated with standard first-line chemotherapy and Avastin. Once their disease worsened, they were randomized to receive either Avastin and a different chemo drug, or the chemo drug and a placebo.

Patients in the Avastin group lived for a median of 11.2 months, compared with 9.8 months for the chemotherapy-alone group. The research was presented on Sunday at a meeting of the American Society of Clinical Oncology.

Genentech said some doctors were already using Avastin as a follow-up regimen for colon cancer patients who had relapsed, and it is talking with regulators about changing the drug's label to include the latest findings.

(Reporting By Deena Beasley; Editing by Peter Cooney)

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