ORLANDO, Fla. --

Genentech's

(DNA)

experimental cancer drug, Avastin, which works by cutting off the blood supply to tumors, slowed tumor growth in patients with advanced cases of kidney cancer.

Results from the 116-patient phase II study were detailed Sunday at the annual meeting of the American Society of Clinical Oncology, although some of the findings were not entirely new, having been released last October. Sunday's Avastin presentation, however, bolstered the case for so-called antiangiogenesis drugs, which are designed to fight cancer by inhibiting the formation of blood vessels that keep tumors alive.

In the study, patients with metastatic kidney cancer were randomized to receive one of two different dose levels of Avastin, or a placebo. Patients who got the higher Avastin dose went about five months before their cancer grew, compared to two months for patients given the placebo -- a statistically significant difference. Patients who received the lower Avastin dose also were able to stave off the growth of their tumors, albeit not as long.

Avastin, though, was only able to shrink tumors in three patients, all of whom received the higher dose.

"We are encouraged by the results of

Avastin in these difficult-to-treat patients," said Dr. James Yang of the National Cancer Institute, the governmental research body that conducted the study. He added, "This is a convincing demonstration that antiangiogenic agents can inhibit tumor growth in patients."

Last October, Genentech reported that patient enrollment in the study was stopped earlier than expected because of the positive results. The company and NCI are working on the design of further studies with kidney cancer patients.

Avastin's potential will get a more thorough working-over later this year when Genentech issues results from a phase III clinical trial testing the drug's efficacy in combination with chemotherapy in breast cancer patients. A phase III test of Avastin in colon cancer patients is also underway, with results expected next year.

Avastin is a monoclonal antibody that targets vascular endothelial growth factor, a protein first discovered by Genentech that seems to play a big role in jumpstarting the formation of new blood vessels for cancerous tumors.

The company will present additional data on Avastin Tuesday, the last day of the ASCO annual meeting. This discussion will be closely watched because it focuses on data from an ASCO research abstract that was seen by Wall Street analysts because of a

leak in April. Shares of Genentech sold off on the leak due to possible safety concerns with Avastin.

Genentech shares closed Friday at $38.25.