An experimental drug that targets the blood supply of tumors can help people with advanced colorectal cancer live longer, according to research presented at a recent oncology meeting. The findings give hope to scientists who have been pursuing this avenue of treatment – known as antiangiogenesis therapy -- for years, without success.

“Our study offers important proof of the philosophy that targeting a tumor’s blood supply can, in fact, inhibit the tumor’s ability to proliferate,” said lead investigator Herbert Hurwitz, MD, of Duke University Medical Center, in a statement.

Hurwitz and his colleagues studied more than 800 people with metastatic colorectal cancer (cancer that had spread to other parts of the body). Half the group received standard chemotherapy for their disease, while the others were treated with standard chemotherapy plus the experimental drug bevacizumab (Avastin), made by Genentech.

Patients receiving Avastin lived about five months longer than patients on the standard regimen alone, Hurwitz reported at the annual meeting of the American Society of Clinical Oncology in Chicago. In addition, more of the Avastin patients saw their tumors shrink, and it took longer for their tumors to resume growing.

Side effects reported in the study were not severe, the researchers said. About 11% of patients developed high blood pressure while taking Avastin, but the condition was manageable with standard medications.

The results are “extremely significant,” said Durado Brooks, MD, director of prostate and colorectal cancer for the American Cancer Society. Advanced disease is very aggressive, he said, and extremely hard to treat with existing chemotherapy regimens.

“Because the outcomes are so poor with advanced disease, it’s marvelous to have a new arrow in our quiver,” Brooks said.

However, he noted that Avastin is not yet available for use (a Genentech statement said it is “discussing plans” to file for FDA approval) and it isn’t a cure.

“The best cure for colon cancer is not to get it,” Brooks said, “so we need to be focusing on early screening to prevent it, or detect it early.”

Screening can help detect colon growths called polyps before they become cancerous. With early detection, Brooks said, five-year survival of colon cancer exceeds 90%; once the disease is advanced, however, five-year survival is only about 10%. Because early colon cancer has few symptoms, only about one-third of cases are detected at this stage.

Colorectal cancer is the third most common cancer in the United States and the second leading cause of cancer deaths. The American Cancer Society estimates that more than 147,000 people will be diagnosed with it this year, and about 57,000 will die from it.

Avastin works against colon cancer by blocking a protein called vascular endothelial growth factor (VEGF). Tumors need the protein to grow and maintain their blood vessels. When VEGF is blocked, the tumor gets less blood, so it shrinks or spreads more slowly.

Several other drugs have tried to attack cancer by choking the tumor’s blood supply, but Avastin appears to be the first one that actually has succeeded, researchers said.

Scientists are hopeful that blocking VEGF can help treat other types of cancer, too. Genetech is studying Avastin for use against kidney cancer, lung cancer, and breast cancer, though initial results of a breast cancer trial were disappointing.

Results from other studies of Avastin for colorectal cancer are also expected soon.

“We want to recognize the contributions of the numerous investigators and the courage of the hundreds of patients who participated (in the clinical trials),” Genentech’s chief medical officer Susan Hellmann, MD, said in a statement.