Updated from 7:45 a.m. EDT

The controversial theory that choking off a tumor's blood supply could be a medically effective way of treat cancer got a huge boost Monday morning -- as did shares of the company reporting the news.

Genentech ( DNA) was up more than 24% in the Instinet premarket after the biotech said its Avastin, along with chemotherapy, proved more effective against colon cancer than even the company's scientists had hoped.

Avastin, which Genentech thinks could be a $1 billion-a-year drug, works via a mechanism known as anti-angiogenesis, in which the growth factor secreted by cancer cells to develop blood vessels is blocked, theoretically leading to a tumor's death.

"This study provides the first Phase III clinical validation of the long-pursued anti-angiogenic hypothesis -- that by targeting a tumor's blood supply, you may impact its viability," said Sue Hellman, Genentech's chief medical officer, in a statement.

The world's No. 2 biotech company said Avastin with chemo exceeded its target for improving survival, and met secondary goals involving the degree and length of response. The phase III study enrolled 900 patients with metastatic colon cancer who had not received prior treatment. Of these patients, 800 were randomized to receive either Avastin plus the standard of care chemotherapy, or a placebo plus the chemotherapy regimen. Results from a smaller study involving a different chemo regimen are expected later this year.

Genentech plans to formally submit its findings at the American Society of Clinical Oncologists, which starts May 31, and then discuss filing with the FDA for clearance to sell Avastin.

Genentech shares were up $9.26, or 24%, to $47.16 on the Instinet premarket session. Protein Design Labs ( PDLI), which receives a royalty on Avastin, was up $2.20, or 19%, to $13.85.